Add small section about editing a profile.

[laundmo]

Editing profiles by using the normal means of changing settings, modifying extensions etc might see obvious to some but still should be explained somewhere.

This PR is just a small section about this fact, and a note about editing the settings.json directly while switching profiles.

[gregvanl]

Thanks.
The final version of this section may differ slightly after an edit pass.

[isidorn]

@laundmo thank you for the PR and thanks @gregvanl for the review and for pinging me.

@sandy081 can you also review these changes please :) Since the "Note:" part feels like a bug that we can fix?

[sandy081]

"Note:" makes sense to me. We do not want to auto close and reopen files on switching profiles. This can be unexpected.