docs(embedder-tool): fix link to relocated MLXEmbedders library

[x-n2o]

Proposed changes

Fixes #483.

Tools/embedder-tool/README.md links to Libraries/Embedders/README.md, which 404s — the embedders library moved to the mlx-swift-lm package as MLXEmbedders. This updates the link to point there, matching the form already used in Applications/MLXChatExample/README.md.

Surfaced by the markdown link check proposed in #479.

Checklist

Put an x in the boxes that apply.

• I have read the CONTRIBUTING document
• I have run pre-commit run --all-files to format my code / installed pre-commit prior to committing changes
• I have added tests that prove my fix is effective or that my feature works
• I have updated the necessary documentation (if needed)

[x-n2o]

Closing — the relocated library target is covered by the .check-links-ignore blocklist in #479 instead.