Merge branch 'ag/send-email-docs'

Documentation for "git send-email" has been updated with a bit more credential helper and OAuth information. * ag/send-email-docs: docs: make the purpose of using app password for Gmail more clear in send-email docs: remove credential helper links for emails from gitcredentials docs: improve formatting in git-send-email documentation docs: add credential helper for yahoo and link Google's sendgmail tool