fix: correct main entry point from lib/index.js to src/index.js (#5)

The main field in package.json was pointing to a non-existent lib/index.js path.
This commit updates it to the actual source location at src/index.js.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude <noreply@anthropic.com>

Author: azu

package.json

@@ -19,7 +19,7 @@
   },
   "license": "MIT",
   "author": "azu",
-  "main": "lib/index.js",
+  "main": "src/index.js",
   "type": "module",
   "bin": {
     "create-textlint-rule-example": "bin/cmd.js"