DOC: Add page for HPC devs/users

From Astropy Coordination Meeting 2021: There is a need for documentation specific to `astropy` usage in HPC for both developers and users.

* Can link to existing "performance" pages currently buried in individual subpackages; e.g., `performance.inc.rst` files in `docs`.
* Links to stories of `astropy` usage and other "Python on HPC" documents.
* Tips and tricks.
* Lessons learned.

p.s. We decided not to do HPC tutorials because historically, those got ignored.

Start by reviewing the existing performance.inc.rst files in the docs and identifying which performance pages should be linked. Gather relevant Astropy usage stories and Python-on-HPC resources, then organize practical tips and lessons learned into an HPC page for developers and users; done means the page covers these materials without adding an HPC tutorial.

Written by the indexing model from the issue text.