docs: add -y to the npx skills install commands

[mwbrooks]

Summary

This pull request removes an interactive prompt from the npx skills install path, so a developer following the documented command gets the skills installed in one step instead of having to answer a question first.

Running the command as documented today stops at a Select skills to install multiselect that starts with nothing selected, so the developer has to arrow, space-select, and confirm before anything is written. Adding -y installs all eight skills straight through. The flag is applied in all three places the command appears: README.md, docs/slack-skills-plugin.md (the page published to docs.slack.dev), and the unreleased changeset that documents this path.

A sentence is added under each code block so the interactive choice is still discoverable: drop -y to pick from the list, or pass -s <skill> to name skills explicitly.

Testing

• Ran npx skills add slackapi/slack-skills-plugin -a opencode in a scratch project: stops at Select skills to install, 0/8 selected, and writes nothing until confirmed.
• Ran npx skills add slackapi/slack-skills-plugin -y -a opencode in the same project: prints Installing all 8 skills and completes with all eight in .agents/skills/ plus a skills-lock.json.
• rumdl check . clean at 19 files.

Notes

• -y is documented by the tool as Skip confirmation prompts, and with -a <agent> already supplied it is the only remaining prompt on this path.
• No new changeset. The existing .changeset/npx-skills-install-path.md documents this same command and has not shipped yet, so its command block is corrected in place rather than adding a second release note about the same flag.
• The docs page has a pre-existing missing-trailing-newline violation that chore: lint the public docs markdown files #145 fixes; left alone here to avoid conflicting with that PR.

Requirements

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.
• I've run make test and the tests pass. Docs-only change; rumdl check . run instead, and the evaluation suite needs GEMINI_API_KEY plus SLACK_MCP_TOKEN, which are not available locally.

[changeset-bot]

⚠️ No Changeset found

Latest commit: f834f4b

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

This PR includes changesets to release 1 package

Name	Type
slack	Patch

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[WilliamBergamin]

-y, I mean yesss do it

[mwbrooks]

Thanks @WilliamBergamin! -y 🚀