Add gm - ghq-style repository manager with built-in fuzzy finder

[jedipunkz]

What

Adds gm to the For Developers section, next to gita.

Why

gm is a ghq-style repository manager written in Rust:

• built-in fuzzy finder with frecency ranking — no ghq list | fzf | cd pipeline needed (Ctrl-G from the shell)
• details pane per repository: remote, branch, working-tree status, visit count, last commits
• first-class git worktree support: browse and check out worktrees, branches, and open GitHub pull requests from the finder
• ghq-compatible layout (`` and ghq.root honored), so existing ghq trees work with no migration
• installable via Homebrew (brew install jedipunkz/gm/gm) or cargo
• MIT licensed, works on macOS and Linux

Checklist

• Entry format matches the list (name, link, one-line description)
• Placed in a sensible section (For Developers, version control tools)
• Active and open-source project

Official site / docs: https://jedipunkz.rocks/gm/