Add documentation for building MCP tools

Introduces a comprehensive guide on creating, testing, and best practices for MCP tools in Symfony applications. Also updates `.gitignore` to stop ignoring the `docs` directory while maintaining other configurations.

Author: klapaudius

.gitignore

@@ -28,6 +28,5 @@ _ide_helper_models.php
 phpunit.xml
 phpstan.neon
 testbench.yaml
-/docs
 /coverage
 /phpunit.coverage.xml