Merge branch 'la/doc-use-of-contacts-when-contributing'

Advertise "git contacts", a tool for newcomers to find people to ask review for their patches, a bit more in our developer documentation. * la/doc-use-of-contacts-when-contributing: SubmittingPatches: demonstrate using git-contacts with git-send-email SubmittingPatches: add heading for format-patch and send-email SubmittingPatches: dedupe discussion of security patches SubmittingPatches: discuss reviewers first SubmittingPatches: quote commands SubmittingPatches: mention GitGitGadget SubmittingPatches: clarify 'git-contacts' location MyFirstContribution: mention contrib/contacts/git-contacts