README: Change badge formatting to reStructuredText

The badges were initially added using the Markdown syntax, which does
not work since this is a reStructuredText file.

README.rst

@@ -1,5 +1,9 @@
-[![Build Status](https://travis-ci.com/LUGGPublic/CG_Labs.svg?branch=master)](https://travis-ci.com/LUGGPublic/CG_Labs)
-[![Build status](https://ci.appveyor.com/api/projects/status/ga1y28ottvmvgif6/branch/master?svg=true)](https://ci.appveyor.com/project/pierremoreau/cg-labs/branch/master)
+|Travis| |AppVeyor|
+
+.. |Travis| image:: https://travis-ci.com/LUGGPublic/CG_Labs.svg?branch=master
+   :target: https://travis-ci.com/LUGGPublic/CG_Labs
+.. |AppVeyor| image:: https://ci.appveyor.com/api/projects/status/ga1y28ottvmvgif6/branch/master?svg=true
+   :target: https://ci.appveyor.com/project/pierremoreau/cg-labs/branch/master
 
 CG_Labs contains the source code for the various Computer Graphics courses
 taught at `Lund University`_ (EDAF80_ and EDAN35_). All assignments of EDAF80