This is a follow-up of https://github.com/docker/distribution/pull/545
and makes some stylistic changes in the CONTRIBUTING document;
- Replaces checkboxes with regular bullets. Because the checkboxes are
read-only for non-contributors, they are presented as 'greyed out',
which makes them harder to see (depending on the browser used)
- Replaces bullets for numbered lists in the "creating an issue" and
"contributing a patch" sections. The numbers make it easier for
readers to track where they left off.
- Cleans up some minor Markdown changes for consistency
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
