DOC: add checklist to MR template
- Add checklist to MR template (see below).
- Change title levels to make headers smaller
- Comment out implementation details sub titles
Avoid forgetting important checks before merging. Easier to recall items of CONTRIBUTING.md
The copyright owner is CNES and has signed the ORFEO ToolBox Contributor License Agreement.
***Check before merging:*** - All discussions are resolved - At least 2