Enable GitHub Pages to redirect to docs.rs

[jonathanhefner]

I've pushed a gh-pages branch that contains a simple redirect to https://docs.rs/rmcp. This will allow users visiting https://modelcontextprotocol.github.io/rust-sdk to be automatically redirected to the official documentation.

To enable this, a maintainer with admin access for the repo needs to:

1. Go to Settings → Pages
2. Under "Build and deployment", set Source to "Deploy from a branch"
3. Select the gh-pages branch and / (root) folder
4. Click Save

The redirect should be live within a few minutes after enabling.

Thank you! 🙏