Add build badges to docs page

Author: mdavezac

docs/index.html

@@ -95,6 +95,9 @@ <h2>News</h2>
     <a href="https://badge.fury.io/py/pys2let">
     <img src="https://badge.fury.io/py/pys2let.svg">
     </a>
+
+    <img src="https://github.com/astro-informatics/s2let/workflows/CMake%20Build/badge.svg">
+    <img src="https://github.com/astro-informatics/s2let/workflows/Python%20Build/badge.svg">
 
   </p>