This PR covers *all* docs source files.
Aiming to be an initial formatting / correcting fix, it:

 - Reformats all docs' headers.
 - Fixes spacing errors.
 - Fixes certain marking errors.

Please note that this PR is far from perfect despite thousands of changes performed.
However, it is essential to format the docs so that MkDocs and other tools can correctly
parse & display them -- and build indexes.

Docker-DCO-1.1-Signed-off-by: O.S. Tezer <ostezer@gmail.com> (github: ostezer)