docs: fix Claude Code install commands in README

[Weili-0234]

The previous claude marketplace add ... command in README does not exist — marketplace is a subcommand of claude plugin, and an explicit claude plugin install smg@smg-dev-guide step is also required. Also documents the in-Claude-Code /plugin equivalents and /reload-plugins to pick up the new skills without a restart.

Problem

The README's Claude Code install instructions don't work. The single command shown — claude marketplace add lightseekorg/smg-dev-guide — has two issues:

1. There is no top-level claude marketplace subcommand. marketplace lives under claude plugin (i.e. claude plugin marketplace …). Running the README's command in a shell just starts an interactive Claude session with marketplace add … as the prompt.

2. Even with the corrected claude plugin marketplace add …, that only registers the marketplace. An explicit claude plugin install smg@smg-dev-guide step is required to actually install the plugin. Trying claude plugin install smg-dev-guide (the marketplace name) fails with Plugin "smg-dev-guide" not found in any marketplace, because the plugin inside the marketplace is named smg.

Solution

Replace the broken one-liner with the correct two-step sequence, and additionally document the in-Claude-Code /plugin equivalents plus /reload-plugins for picking up the new skills without restarting.

Changes

• README.md — Claude Code install section:
  • Replaced claude marketplace add … with claude plugin marketplace add … followed by claude plugin install smg@smg-dev-guide.
  • Added the in-Claude-Code /plugin marketplace add … + /plugin install … equivalents.
  • Noted /reload-plugins (or restart) to load the skills after install.

Affected Skills

• smg:map
• smg:contribute
• smg:review-pr
• smg:implement
• Recipe files (list which)
• Command router (smg.md)
• Plugin config (plugin.json)

Checklist

• Follows conventional commit title format
• Commit(s) are signed off (git commit -s)
• Tested with claude plugins add . locally
• Skill triggers correctly on intended prompts
• No broken @file.md references in skills