Docs: Add aspell wordlist to improve spellchecking

Docs: Add aspell wordlist to improve spellchecking

To spellcheck the docs:

  - Go into the docs/ directory.
  - Copy the wordlist to your home directory (making a backup of your
    existing wordlist, if you have one):
    - cp --backup .aspell.en.pws ~/
  - Run 'aspell' over all AsciiDoc files, except release notes. Don't
    need to create backup files, since we're under version control. This
    runs the interactive spellchecker; use it to fix incorrect words, or
    add new correct words to the wordlist:
    - for f in $(find . -name '*.adoc' -and ! -name 'RELEASE*'); do
      aspell check --ignore-case --dont-backup $f; done
  - Review your changes:
    - git diff
  - Commit spelling corrections in one commit. Noteworthy changes should
    be included in the commit message.
  - Commit changed wordlist in a separate commit.

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