Improve Getting Started for users

[loleg]

Currently the documentation still focuses on the needs of a developer. For a sysadmin who has the task of installing Proxeus, the steps are not very clear. In particular, the Docker support and One-Click options need to be more prominent.

The Help/Support of the application currently links to the Google version of the Handbook. Instead, we should move the handbook.md chapter also into the docs, moving the image files into their own subfolder (docs/images/handbook/*.png)

Additional ideas can be found in the comments from @Halil-Kuray at https://github.com/orgs/ProxeusApp/discussions/15

[loleg]

There are a couple of places where we still have the old link.