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

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