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).