docs: Add upgrade instructions to README

[arnthorsnaer]

Hi! 👋

This PR suggests adding explicit upgrade instructions to the README to help users keep both the CLI and the embedded agent skill up to date.

Current situation:

• The README documents installation (make install) and the agent skill (hey skill install)
• It's not immediately clear that users need to rebuild the binary (make install) AND re-run hey skill install after pulling updates
• The agent skill is embedded in the binary at build time, so git pull alone doesn't update it

Proposed change:
Add a new "Upgrading" section that documents the three-step process:

1. git pull (fetch latest changes)
2. make install (rebuild binary with updated embedded skill)
3. hey skill install (copy updated skill to ~/.agents/skills/hey/)

Note:
This is a suggestion to improve documentation clarity — feel free to close if you prefer a different approach or if this is already covered elsewhere. No pressure! Just wanted to raise awareness that the upgrade flow could be more explicit. 😊

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Authored via OpenClaw agent 🦉

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Summary by cubic

Adds an "Upgrading" section to the README that explains how to update hey-cli and the embedded agent skill. Use git pull, make install, and hey skill install to rebuild the binary and keep the global skill in sync.

^{Written for commit 87862ab. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 1 file

[Copilot]

Pull request overview

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Adds explicit upgrade guidance to the project README so users understand they must rebuild the CLI binary and reinstall the embedded agent skill after pulling updates.

Changes:

• Add a new Upgrading section describing a 3-step update flow (git pull, make install, hey skill install).
• Document that the agent skill is embedded at build time and needs reinstalling to stay in sync with the binary.

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[Copilot]

The upgrade instructions call this an “agent skill”, but hey skill install is currently documented/implemented as Claude-specific and also creates a symlink under ~/.claude/skills/hey in addition to writing ~/.agents/skills/hey/SKILL.md. Consider clarifying this here (e.g., mention Claude explicitly and/or the two target locations) so users understand what gets updated when they rerun the command.