Improve "security reports" section in contribution docs.

Signed-off-by: Solomon Hykes <solomon@docker.com>
In contribution docs, emphasize that bug reports are appreciated!

Signed-off-by: Solomon Hykes <solomon@docker.com>
Move GOVERNANCE.md to hack/

Signed-off-by: Solomon Hykes <solomon@docker.com>
Merge pull request #9177 from shykes/hack-docs-small-improvements

Small improvements to contribution docs