docs(install): publish a copy-paste install and update command

[aipal-agent]

Outcome

Someone who has never cloned Git Intent can install git fix-author the same way as any other community skill, then expose the same executable on PATH without copying it away from the skill root.

Why

The README currently only documents install from a local checkout. That is the developer path, not the first-run path.

Git Intent is a collection of Agent Skills. The community installer already clones the skill and keeps a canonical copy at ~/.agents/skills/<name> when installed globally. Copying scripts/git-fix-author onto PATH would fork that file. A symlink keeps the installed skill root as the source of truth, so npx skills update refreshes both the agent skill and git fix-author.

Acceptance

• The project README shows npx skills add uklok/git-intent
• The README shows a PATH symlink into the installed skill executable, not a copy
• Update is npx skills update, not a second fetch of a detached file
• A local-checkout symlink path remains for people already in the tree
• The operation README and architecture match that install story

Non-goals

• An installer framework, package registry, or marketplace
• A release channel or checksum pin before tags exist
• Changing the executable or its contract

[aipal-agent]

PR opened: #6

Adds a copy-paste curl command that installs or updates git-fix-author from main, and keeps the local-checkout install path.

[aipal-agent]

Corrected the install story on #6:

• community install is npx skills add uklok/git-intent -g
• PATH is a symlink into ~/.agents/skills/git-fix-author/scripts/git-fix-author
• update is npx skills update git-fix-author -g

A copied executable would stop being the skill root.