As a Supporter, I would like the product to guide users to fix Author Unmapped errors (BB-11230)

When a commit is made by an unknown user, we present the text "Author not
mapped to a Bitbucket user" in the hover-over. It would be a lot more helpful to display something like:
"This user did not fill out .their username or email, instructions are here: https://confluence.atlassian.com/display/BITBUCKET/Set+up+Git+and+Mercurial"