[WIP] Updates to the man pages for capabilities.

[burnMyDread]

- What I did
Added additional documentation related to the new capabilities flag.
moby/moby#39297 (comment)
- How I did it
Docs change.
- How to verify it
Docs change.
- Description for the changelog

Adding documentation for the change log.

- A picture of a cute animal (not mandatory but encouraged)

[GordonTheTurtle]

Please sign your commits following these rules:
https://github.com/moby/moby/blob/master/CONTRIBUTING.md#sign-your-work
The easiest way to do this is to amend the last commit:

$ git clone -b "39149-Default-Capabilites" git@github.com:burnMyDread/cli.git somewhere
$ cd somewhere
$ git commit --amend -s --no-edit
$ git push -f

Amending updates the existing PR. You DO NOT need to open a new one.

[codecov-io]

Codecov Report

Merging #1964 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1964   +/-   ##
=======================================
  Coverage   56.72%   56.72%           
=======================================
  Files         310      310           
  Lines       21800    21800           
=======================================
  Hits        12367    12367           
  Misses       8518     8518           
  Partials      915      915