docs: shields that are actually useful

It is unnecessary to point to CI, or to indicate the doc version. Instead, we
link directly to the source code. Also, we improve the icon colors and general
appearance.

README.rst

@@ -10,33 +10,31 @@ Tutor: the docker-based Open edX distribution designed for peace of mind
   :width: 500px
   :align: center
 
-|
-
-.. image:: https://github.com/overhangio/tutor/actions/workflows/release.yml/badge.svg
-    :alt: Release build status
-    :target: https://github.com/overhangio/tutor/actions/workflows/release.yml
+.. image:: https://img.shields.io/static/v1?logo=github&label=Git&style=flat-square&color=brightgreen&message=Source%20code
+  :alt: Source code
+  :target: https://github.com/overhangio/tutor
 
-.. image:: https://img.shields.io/badge/docs-current-blue.svg?style=flat-square
-    :alt: Documentation
-    :target: https://docs.tutor.overhang.io
+.. image:: https://img.shields.io/static/v1?logo=discourse&label=Forums&style=flat-square&color=ff0080&message=discuss.overhang.io
+  :alt: Forums
+  :target: https://discuss.overhang.io
 
-.. image:: https://img.shields.io/github/issues/overhangio/tutor.svg?style=flat-square
-    :alt: GitHub issues
-    :target: https://github.com/overhangio/tutor/issues
+.. image:: https://img.shields.io/static/v1?logo=readthedocs&label=Documentation&style=flat-square&color=blue&message=docs.tutor.overhang.io
+  :alt: Documentation
+  :target: https://docs.tutor.overhang.io
 
-.. image:: https://img.shields.io/github/issues-closed/overhangio/tutor.svg?colorB=brightgreen&style=flat-square
-    :alt: GitHub closed issues
-    :target: https://github.com/overhangio/tutor/issues?q=is%3Aclosed
+.. image:: https://img.shields.io/pypi/v/tutor?logo=python&logoColor=white
+  :alt: PyPI releases
+  :target: https://pypi.org/project/tutor
 
 .. image:: https://img.shields.io/github/license/overhangio/tutor.svg?style=flat-square
-    :alt: AGPL License
-    :target: https://www.gnu.org/licenses/agpl-3.0.en.html
+  :alt: AGPL License
+  :target: https://www.gnu.org/licenses/agpl-3.0.en.html
 
-.. image:: https://img.shields.io/twitter/follow/overhangio
-    :alt: Follow us on Twitter
-    :target: https://twitter.com/overhangio/
+.. image:: https://img.shields.io/static/v1?logo=twitter&label=Twitter&style=flat-square&color=1d9bf0&message=@overhangio
+  :alt: Follow us on Twitter
+  :target: https://twitter.com/overhangio/
 
-.. image:: https://img.shields.io/youtube/channel/views/UCe_p_Axq3PjRnbTqFZDY_iQ?label=Overhang.IO%20on%20Youtube
+.. image:: https://img.shields.io/static/v1?logo=youtube&label=YouTube&style=flat-square&color=ff0000&message=@overhangio
     :alt: Follow us on Youtube
     :target: https://www.youtube.com/c/OverhangIO