Add links to IDAES etc. on every page

[dangunter]

In the Sphinx conf.py file, you can set a variable rst_epilog to a string whose contents will be interpreted as reStructuredText and appended at the bottom of every page of documentation. This could be used to add a link to IDAES and any other relevant dependencies on every page. It could also be used, as in the IDAES project, to define some shortcuts (substitutions) so links could be easily inserted and, if changed, updated in one place. See https://github.com/IDAES/idaes-pse/blob/main/docs/conf.py

[ksbeattie]

Here is an example of this being used in IDAES: https://idaes-pse.readthedocs.io/en/stable/tutorials_examples.html

[bknueven]

Related: if we're linking heavily into IDAES docs (a good idea), we should minimally running the docs linkcheck.

[ksbeattie]

@dangunter suggests that another approach would be to have separate "dependencies" page listing what our dependencies are and links to them.