Fix title of roadmap page, and show a consistent list

docs/devel/roadmap/index.rst

-Previous roadmaps
------------------
+.. _roadmaps:
 
-This page lists our archived roadmaps. You can also have a look at our current roadmap: :ref:`roadmap-current`.
+Current and past roadmaps
+-------------------------
 
 .. toctree::
    :maxdepth: 2
    :titlesonly:
 
+   roadmap-2022
    roadmap-2021