docs(readme): link the documentation site from the header

[monody0007]

What this changes

Adds one centered line under the tagline: Docs and guides: tslink.md, linking https://tslink.md.

The README currently has no link to the documentation site; the only connection is the repository's homepage field. Directory listings (awesome-mcp-servers, mcpservers.org) and search results land readers on this repository, so the header is where they need a way to reach the guides. No other text, heading or translated README changes.

How it was verified

• git diff --stat: README.md, 1 insertion.
• No test reads README.md (grep -rn README.md over Go, shell, Python and workflow files finds only unrelated fixtures and release tooling).
• https://tslink.md returns HTTP 200.

Checklist

• One logical change. Formatting changes are not mixed with behaviour changes.
• An issue was opened first to discuss this change. (Maintainer docs-only change.)
• Tests cover the new behaviour, including the case that fails without it. (No behaviour change.)
• Documentation is updated if behaviour changed.
• Local checks pass: go build ./... && go vet ./... && go test ./... (Not run: README-only change.)