docs: add .skill package installation instructions

Document both CLI and manual extraction methods for installing
.skill packages, covering VS Code extension users without the
claude CLI.

claude-code-tools.md

@@ -23,6 +23,25 @@ Up-to-date documentation and code examples for any library, available directly i
 
 Skills are a different extension mechanism from MCPs. They are prompt-based extensions invoked via `/skill-name` commands directly within Claude Code — no external server required.
 
+### Installing `.skill` packages
+
+Skills are distributed as `.skill` files (ZIP archives containing a `SKILL.md` and optional scripts).
+
+**Option 1 — CLI** (if `claude` command is available):
+
+```bash
+claude skill install --scope user my-skill.skill
+```
+
+**Option 2 — Manual extraction** (works everywhere, including VS Code extension):
+
+```bash
+# Python one-liner
+python -c "import zipfile; zipfile.ZipFile('my-skill.skill').extractall('$HOME/.claude/skills')"
+```
+
+Skills are extracted into `~/.claude/skills/<skill-name>/`. They become available in the next Claude Code session.
+
 ### AST Index
 
 Fast code search skill for Claude Code — find classes, symbols, usages, implementations, and more across large codebases using AST parsing.