docs: Documentation updates

[pawamoy]

Meta issue for tracking documentation improvements.

• limitation with footnotes, references (see Document docstring parsing limitations pytkdocs#26)
• how to document enumeration values
• recommendation: giving a heading to each object, even modules
• suggest https://github.com/analog-garage/mkdocstrings-python-xref as alternate handler with relative cross-refs
• suggest https://github.com/jcayers20/mkdocs-autoapi for automatic generation of pages (see Autodoc-like project layout mkdocstrings#389)
• see all issues with docs label
• Make it more prominent that show_submodules is needed for recursivley documenting submodules (see docs: Make it more prominent that show_submodules is needed for recursivley documenting submodules #146)