docs(workspaces): Document --include use case

Author: oskarols

.yarn/versions/a2ec75bc.yml

@@ -0,0 +1,2 @@
+declined:
+  - "@yarnpkg/plugin-workspace-tools"

packages/plugin-workspace-tools/sources/commands/foreach.ts

@@ -59,6 +59,10 @@ export default class WorkspacesForeachCommand extends BaseCommand {
     [
       `Run the build script on several packages and all their dependencies, building dependencies first`,
       `yarn workspaces foreach -Rpt --from '{workspace-a,workspace-b}' run build`,
+    ],
+    [
+      `Run the build script only on a specific set of packages`,
+      `yarn workspaces foreach -A --include '{workspace-a,workspace-b}' run build`,
     ]],
   });