Fix references from 'packages/*' to 'platform/*' in READMEs (#23498)

webapp/README.md

@@ -11,7 +11,7 @@ To interact with a workspace using npm, such as to add a dependency or run a scr
 npm add react --workspace=boards
 
 # Build multiple packages
-npm run build --workspace=packages/client --workspace=packages/components
+npm run build --workspace=platform/client --workspace=platform/components
 
 # Test all workspaces
 npm test --workspaces
@@ -25,4 +25,4 @@ To install dependencies for a workspace, simply run `npm install` from this fold
 ## Useful Links
 
 - [Developer setup](https://developers.mattermost.com/contribute/developer-setup/), now included with the Mattermost server developer setup
-- [Web app developer documentation](https://developers.mattermost.com/contribute/more-info/webapp/)
+- [Web app developer documentation](https://developers.mattermost.com/contribute/more-info/webapp/)