Add recommendation to use 'Edit' mode
Before this commit, the recommended method was to use 'WebIDE' option. For our less technical contributors it could be complicated to use:
- it "allows" for changes on official repo and only throws errors when the user wants to commit them,
- by default, it commits changes on master of the fork instead of creating new branch, which makes it harder to merge later in some circumstances,
- it doesn't create merge requests automatically. After this commit, the suggested method is to use 'Edit' mode, which doesn't have those issues (although doesn't allow editing multiple files at once).