Clarify MCP vs Skills distinction in README

Separate AST Index into its own Skills section, add descriptions
for both extension mechanisms, and fix markdown lint warnings.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

README.md

@@ -4,20 +4,28 @@ A collection of interesting and useful facts, tips, and tools for working with C
 
 ## MCP Servers
 
+MCP (Model Context Protocol) servers are external processes that provide tools to Claude Code via a standardized protocol. They run alongside your session and extend Claude's capabilities.
+
 ### Context7
 
 Up-to-date documentation and code examples for any library, available directly in your Claude Code session.
 
-- **Website:** https://context7.com/
+- **Website:** <https://context7.com/>
 - **Setup:**
+
   ```bash
   claude mcp add --scope user --transport http context7 https://mcp.context7.com/mcp --header "CONTEXT7_API_KEY: <YOUR_API_KEY>"
   ```
 
 - **Note:** API key can be created for free after signing in at [context7.com](https://context7.com/)
 
+## Skills (Slash Commands)
+
+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.
+
 ### AST Index
 
-Fast code search skill for Claude Code — find classes, symbols, usages, implementations, and more across large codebases.
+Fast code search skill for Claude Code — find classes, symbols, usages, implementations, and more across large codebases using AST parsing.
 
-- **Repository:** https://github.com/defendend/Claude-ast-index-search
+- **Repository:** <https://github.com/defendend/Claude-ast-index-search>
+- **Usage:** Invoke with `/ast-index` or related commands like "find class", "search for symbol", etc.