Solve 368#issue-1464483861

[flochre]

update platform.py and README.md to follow the updated REP-2000 - delete dashing add humble update rolling

Solve this issue https://github.com/ros-tooling/cross_compile/issues/368#issue-1464483861

[christophebedard]

Could you also update the tests? Specifically:

• https://github.com/ros-tooling/cross_compile/blob/0fb22b8248d554d5e3021a87eacf5684b732676b/.github/workflows/e2e_test.yml#L19
• https://github.com/ros-tooling/cross_compile/blob/0fb22b8248d554d5e3021a87eacf5684b732676b/.github/workflows/pip_e2e_test.yml#L17

[christophebedard]

This has been superseded by (and cherry-picked into) #372, so I'll close this. Thanks for the contribution.