Add mission statement and other good things to the README #148

Describe the task

We should update the existing README and add some things that were requested or are missing like:

• Short paragraph of what XLibre is
• Motivation/Reasons to fork
• Mission statement
• Project achievements so far (Top 3 or so)
  • with screenshots where applicable
    • Add XLibre screenshot sharing thread to Show and Tell discussions #210
• Links to the release notes in the mailing list
• Link to the NEWS file containing a simple changelog
  • Create a public changelog #141
• What‘s next
• Switching to XLibre reference
  • only brief instructions
  • postponed: Add directions on how to switch to XLibre xserver#210
• (Short) build instructions
  • including supported platforms (or keep it separate?)
  • link to the wiki for details
    • Document how to build and start XLibre xserver#63
    • Easy-to-understand installation manual xserver#280
• Section about compatibility
  • Mention API/ABI stability aspects
  • Mention the dependency on the project provided drivers
  • Mention efforts to ensure compatibilty with Nvidia driver
  • Add a Compatibility page to the wiki xserver#436
• Upgrade notices
• Contributing section
  • Call to action for driver testers
    • Create a XLibre Test Drivers program · X11Libre · Discussion #240
  • postponed: Call to action for test engineers to create test cases
  • postponed: Call to action for continious integration geeks
  • Links to the existing packages and package related discussions
    • Consolidate support for packaging XLibre by our community #135
  • Call to action for packagers
    • X11Libre Xlibre On Other Distributions · Discussions · GitHub
  • Call for ideas (link to Discussions/Ideas)
    • Add more structure to the "Ideas" discussions #224
    • Add discussion forms to "Ideas" discussions #225
  • Call to action for "Show and Tell"
    • Add XLibre screenshot sharing thread to Show and Tell discussions #210
  • Link to awesome lists?
• License?
• Outro

Maybe more, maybe less.

It should be done because

We should guide our users and potential contributors to the information listed aboves. This is the outcome of several discussions and issues which will get linked here.

Addtional Information

Please only comment on this issue if you have something new that is related to this topic and has not been said already.

Extra fields

• I have checked the existing issues
• I have read the Contributing Guidelines
• I'd like to work on this issue