Backport: chore: add readme for @ai-sdk/mcp

[github-actions]

This is an automated backport of #15445 to the release-v6.0 branch. FYI @aayush-kapoor
This backport has conflicts that need to be resolved manually.

git cherry-pick output

CONFLICT (modify/delete): .github/konsistent.json deleted in HEAD and modified in 5ca54e753 (chore: add readme for @ai-sdk/mcp (#15445)).  Version 5ca54e753 (chore: add readme for @ai-sdk/mcp (#15445)) of .github/konsistent.json left in tree.
error: could not apply 5ca54e753... chore: add readme for @ai-sdk/mcp (#15445)
hint: After resolving the conflicts, mark them with
hint: "git add/rm <pathspec>", then run
hint: "git cherry-pick --continue".
hint: You can instead skip this commit with "git cherry-pick --skip".
hint: To abort and get back to the state before "git cherry-pick",
hint: run "git cherry-pick --abort".
hint: Disable this message with "git config set advice.mergeConflict false"