Update contributing instructions to match GitHub UI

[thatrobotdev]

Changes contributing instructions to match GitHub UI for Build and deployment.

The instructions say:

3. Enable GitHub Pages
   • Go to Settings > Pages in your forked repository.
   • Under Source, select the branch you want to deploy (e.g., main) and the folder (e.g.,/docs).
   • Click Save to enable GitHub Pages.

but GitHub UI has the branch selection under the "Branch" section instead:

So this updates the instructions to match.

[Classic298]

thanks