[Headscale] Add guide with setup and usage

[dotWee]

This pull request introduces a new guide for setting up and using Headscale, an open-source, self-hosted implementation of the Tailscale control server. The guide provides detailed instructions on installation, configuration, and integration with Uberspace's web backend, including prerequisites, setup steps, and usage examples.

New Guide for Headscale Setup and Usage:

• Guide Overview and Licensing:

  • Added an introduction to Headscale, highlighting its purpose as a self-hosted Tailscale control server using the WireGuard protocol.
  • Included licensing information (BSD-3-Clause License) and links to the official Headscale GitHub repository.

• Installation Instructions:

  • Detailed steps for downloading and installing the Headscale binary, setting up directories, and configuring the application.

• Configuration for Uberspace Integration:

  • Provided specific configuration details for running Headscale behind Uberspace's web backend, including disabling TLS and enabling WebSocket support.

• Daemon Setup and Testing:

  • Instructions for creating and managing a supervisord configuration file to run Headscale as a service, with guidance on testing and troubleshooting.

• Initial Usage and Updates:

  • Explained how to create users, generate preauth keys, and register devices with Headscale

[dotWee]

@luto @nichtmax is there anything left to do to get this merged?