docs: move full-clone footnote from README to CONTRIBUTING

The "Contributing or need full history?" note is for contributors, not
for someone following the README install flow. Moved into CONTRIBUTING's
Quick start section where it fits next to the existing clone command,
with a tip to upgrade an existing shallow clone via
\`git fetch --unshallow\`.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

CONTRIBUTING.md

@@ -9,11 +9,13 @@ gstack skills are Markdown files that Claude Code discovers from a `skills/` dir
 That's what dev mode does. It symlinks your repo into the local `.claude/skills/` directory so Claude Code reads skills straight from your checkout.
 
 ```bash
-git clone <repo> && cd gstack
+git clone https://github.com/garrytan/gstack.git && cd gstack
 bun install                    # install dependencies
 bin/dev-setup                  # activate dev mode
 ```
 
+> **Full clone vs shallow.** The README's user-facing install uses `--depth 1` for speed. As a contributor, use a full clone (no `--depth` flag) — you'll need history for `git log`, `git blame`, `git bisect`, and reviewing PRs against earlier versions. If you already have a `--depth 1` clone from following the README, promote it to a full clone with `git fetch --unshallow`.
+
 Now edit any `SKILL.md`, invoke it in Claude Code (e.g. `/review`), and see your changes live. When you're done developing:
 
 ```bash

README.md

@@ -62,11 +62,6 @@ No vendored files in your repo, no version drift, no manual upgrades. Every Clau
 
 Swap `required` for `optional` if you'd rather nudge teammates than block them.
 
-> **Contributing or need full history?** The commands above use `--depth 1` for a fast install. If you plan to contribute or need full git history, do a full clone instead:
-> ```bash
-> git clone https://github.com/garrytan/gstack.git ~/.claude/skills/gstack
-> ```
-
 ### OpenClaw
 
 OpenClaw spawns Claude Code sessions via ACP, so every gstack skill just works