doc: add multiple package entries example (#1416)

Author: marvinhagemeister

runtime/fundamentals/workspaces.md

@@ -147,6 +147,33 @@ Deno workspaces are flexible and can work with Node packages. To make migration
 for existing Node.js projects easier you can have both Deno-first and Node-first
 packages in a single workspace.
 
+### Multiple package entries
+
+So far, our package only has a single entry. This is fine for simple packages,
+but often you'll want to have multiple entries that group relevant aspects of
+your package. This can be done by passing an `object` instead of a `string` to
+`exports`:
+
+```json title="my-package/deno.json"
+{
+  "name": "@scope/my-package",
+  "version": "0.3.0",
+  "exports": {
+    ".": "./mod.ts",
+    "./foo": "./foo.ts",
+    "./other": "./dir/other.ts"
+  }
+}
+```
+
+The `"."` entry is the default entry that's picked when importing
+`@scope/my-package`. Therefore, the above `deno.json` example provides the
+folowing entries:
+
+- `@scope/my-package`
+- `@scope/my-package/foo`
+- `@scope/my-package/other`
+
 ### Migrating from `npm` workspaces
 
 Deno workspaces support using a Deno-first package from an existing npm package.
@@ -278,7 +305,7 @@ root and its members:
 | fmt.singleQuote    | ✅        | ✅      | Package takes priority over workspace.                                                                                                                                                                                                                                                                 |
 | fmt.proseWrap      | ✅        | ✅      | Package takes priority over workspace.                                                                                                                                                                                                                                                                 |
 | fmt.semiColons     | ✅        | ✅      | Package takes priority over workspace.                                                                                                                                                                                                                                                                 |
-| fmt.options.*      | ⚠️        | ❌      | Deprecated                                                                                                                                                                                                                                                                                             |
+| fmt.options.\*     | ⚠️        | ❌      | Deprecated                                                                                                                                                                                                                                                                                             |
 | nodeModulesDir     | ✅        | ❌      | Resolution behaviour must be the same in the entire workspace.                                                                                                                                                                                                                                         |
 | vendor             | ✅        | ❌      | Resolution behaviour must be the same in the entire workspace.                                                                                                                                                                                                                                         |
 | tasks              | ✅        | ✅      | Package tasks take priority over workspace. cwd used is the cwd of the config file that the task was inside of.                                                                                                                                                                                        |
@@ -291,7 +318,7 @@ root and its members:
 | bench.exclude      | ✅        | ✅      |                                                                                                                                                                                                                                                                                                        |
 | bench.files        | ⚠️        | ❌      | Deprecated                                                                                                                                                                                                                                                                                             |
 | lock               | ✅        | ❌      | Only a single lock file may exist per resolver, and only resolver may exist per workspace, so conditional enablement of the lockfile per package does not make sense.                                                                                                                                  |
-| unstable           | ✅        | ❌      | For simplicities sake, we do not allow unstable flags, because a lot of the CLI assumes that unstable flags are immutable and global to the entire process. Also weird interaction with DENO_UNSTABLE_* flags.                                                                                         |
+| unstable           | ✅        | ❌      | For simplicities sake, we do not allow unstable flags, because a lot of the CLI assumes that unstable flags are immutable and global to the entire process. Also weird interaction with DENO_UNSTABLE_\* flags.                                                                                        |
 | name               | ❌        | ✅      |                                                                                                                                                                                                                                                                                                        |
 | version            | ❌        | ✅      |                                                                                                                                                                                                                                                                                                        |
 | exports            | ❌        | ✅      |                                                                                                                                                                                                                                                                                                        |