Docs: Fix docs build warnings

Docs: Fix docs build warnings

This commit fixes the following kinds of warnings given by asciidoc when
building the docs HTML:

  - Incorrect header level
  - Incorrect list numbering
  - List numbering interrupted by an image (needs '+' on blank lines)
  - In one case, a list used '1)' style numbering, which AsciiDoc
    doesn't recognize. This commit corrects that, even though it caused
    no errors.

These are minor issues, but fixing them is easy and prevents future
confusion and errors.

Signed-off-by: Remington Steed <rjs7@calvin.edu>