Add instructions on compilation for ROS2 Humble on Ubuntu 22

[JustusBraun]

No description provided.

[Copilot]

Pull request overview

This PR adds compilation instructions and CMake configuration changes to support building the MeshMPPI package on Ubuntu 22 with ROS2 Humble, which ships with an older GCC version that lacks full C++23 support.

Key Changes:

• Added CMake version check for CMP0135 policy to avoid errors on older CMake versions
• Added GCC version validation requiring GCC 13+ for proper C++23 support
• Included detailed instructions in README for installing GCC 13 on Ubuntu 22

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
mesh_mppi/CMakeLists.txt	Adds conditional CMake policy setting, default Release build type, and GCC version enforcement to ensure C++23 compatibility
README.md	Adds collapsible section with Ubuntu 22/ROS2 Humble compilation instructions including GCC 13 installation steps

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