Adjust settings documentation "don't use project URL as settings URL"

[jan-vcapgemini]

We need to adjust our setup documentation so that users don't think that they should add their project URL as a settings URL when they create a new project.

[hohwille]

See also #850

Instead of adding more documentation that most users never read - how about checking if the URL contains settings and print a warning if it doesn't, that the user must confirm.
Then our projects are more or less forced to name their git settings repos reasonable and users that do stupid things get educated instead of being left in the rain.