Fix broken link formatting on start page (#691)

Author: henningkayser

index.rst

@@ -41,5 +41,5 @@ Help us improve these docs and we'll be happy to include you here also!
 Corporate Sponsorship
 ---------------------
 
-* The tutorials had a major update in 2018 during a code sprint sponsored by Franka Emika in collaboration with <a href="https://picknik.ai/">PickNik Robotics</a> (`Check out the blog post! <http://moveit.ros.org/moveit!/ros/2018/02/26/tutorials-documentation-codesprint.html>`_)
-* The tutorials had another major update in 2022 during a doc-a-thon sponsored by <a href="https://picknik.ai/">PickNik Robotics</a>
+* The tutorials had a major update in 2018 during a code sprint sponsored by Franka Emika in collaboration with `PickNik Robotics <https://picknik.ai/>`_ (`Check out the blog post! <http://moveit.ros.org/moveit!/ros/2018/02/26/tutorials-documentation-codesprint.html>`_)
+* The tutorials had another major update in 2022 during a doc-a-thon sponsored by `PickNik Robotics <https://picknik.ai/>`_.