I'm almost done with the tutorial page. I add some general information about CMake and cross-compilation.
I'm still thinking on the best way to upstream the cross-compilation related files. The last idea is to create a `ros2/crosscompile` repo, which will contains a package with the same name.
This repo will come by default with a COLCON_IGNORE, allowing us to add it to the ros2.repos file. Native compilation will not be affected, and cross-compilation would be possible by simply removing this file.
This approach allows us to add a script to generate the sysroot with colcon, before the other packages.
Regarding the cross-compilation itself, I still have to ignore the following packages: