Stable docs has warning saying development build

Currently, on the index.html page of the stable docs, there is a warning message saying the following:

.. warning::

      You are viewing documentation for a development build of PESummary.
      This version may include unstable code, or breaking changes relative
      the most recent stable release.
      To view the documentation for the latest stable release of PESummary,
      please `click here <../stable_docs/index.html>`_.

This warning message is required for the unstable docs. Maybe this should be either inserted into the index.html of the unstable docs by the build_docs.sh script or alternatively removed by the build_docs.sh script for the stable version of the docs.