docs: update GitHub Actions workflow for iOS (#25)

This pull request updates the example GitHub Actions workflow for iOS by adding a step to install Watchman. It turns out that this dramatically speeds up the file-crawling process and makes Harness run much faster.

Author: V3RON

website/src/docs/guides/ci-cd.md

@@ -158,6 +158,10 @@ jobs:
           node-version: '18'
           cache: 'pnpm'
 
+      # Watchman dramatically speeds up file crawling for large projects
+      - name: Install Watchman
+        run: brew install watchman
+
       - name: Install dependencies
         run: pnpm install