Add descriptions (minimal docs) to ui

[anbraten]

Problem

There are currently quite some options inside the settings without any description. Only place you "could" eventually find descriptions for these settings is in the documentation.

Repo settings

For example Project Visibility Internal vs Private could be unclear to users.

Registries

Add some info box what registries / secrets are and how they effect your CI.

For example for secrets:

Secrets are exposed to your pipeline steps and plugins as uppercase environment variables and 
can therefore be referenced in the commands section of your pipeline.
A secret with the name `test` would be accessible as `TEST` inside your CI step. 
Have a look to the [docs](...) for more information.

Suggestion

To keep things simple and to not need to find the correct place in the docs, I would suggest to add some kind of description explaining each option to all possible places where settings are used.

Example for Project Settings > Protected: