Add MCP Toplist rank badge

[chrstphe]

Hi! MCP Toplist tracks 81,852 MCP servers across the major
registries, and Webcomponents React is currently ranked #563.

This PR adds a small live badge to your README showing that rank — it updates
automatically as the leaderboard changes:

Totally fine to close if you'd rather not — and if you'd like your server's
data corrected or removed from the leaderboard, just say so here or open an
issue at the site. Thanks for building Webcomponents React!

[cla-assistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[Lukas742]

Hi @chrstphe, thanks for the PR!

We'd prefer to keep the README badges limited to ones tied to the package itself (build, version, coverage) and project infrastructure, so we'll pass on this one. A live badge pulling from an external leaderboard also adds a dependency outside our control that we'd rather avoid. No issue with the listing itself 🙂