add 2.3 updates for local node modules (#1669)

Co-authored-by: Phil Hawksworth <phil@deno.com>

Author: thisisjofrank

runtime/fundamentals/modules.md

@@ -329,11 +329,38 @@ Limitations:
 
 ### Overriding NPM packages
 
-We plan to support NPM packages with the patch functionality described above,
-but until then if you have a `node_modules` directory, `npm link` can be used
-without change to accheive the same effect. This is typically done with
-`{ "nodeModulesDir": "manual" }` set in the `deno.json` file. See also the
-documentation on [`node_modules`](/runtime/fundamentals/node/#node_modules)
+Deno supports patching npm packages with local versions, similar to how JSR
+packages can be patched. This allows you to use a local copy of an npm package
+during development without publishing it.
+
+To use a local npm package, configure the `patch` field in your `deno.json`:
+
+```json
+{
+  "patch": [
+    "../path/to/local_npm_package"
+  ],
+  "unstable": ["npm-patch"]
+}
+```
+
+This feature requires a `node_modules` directory and has different behaviors
+depending on your `nodeModulesDir` setting:
+
+- With `"nodeModulesDir": "auto"`: The directory is recreated on each run, which
+  slightly increases startup time but ensures the latest version is always used.
+- With `"nodeModulesDir": "manual"` (default when using package.json): You must
+  run `deno install` after updating the package to get the changes into the
+  workspace's `node_modules` directory.
+
+Limitations:
+
+- Specifying a local copy of an npm package or changing its dependencies will
+  purge npm packages from the lockfile, which may cause npm resolution to work
+  differently.
+- The npm package name must exist in the registry, even if you're using a local
+  copy.
+- This feature is currently behind the `unstable` flag.
 
 ### Overriding HTTPS imports