[PATCH] Documentation: add instructions to help setup gmail 2FA

[Michael Rappazzo <rappazzo@gmail.com>]

For those who use two-factor authentication with gmail, git-send-email
will not work unless it is setup with an app-specific password. The
example for setting up git-send-email for use with gmail will now
include information on generating and storing the app-specific password.
---
 Documentation/git-send-email.txt | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/Documentation/git-send-email.txt b/Documentation/git-send-email.txt
index 771a7b5..edbba3a 100644
--- a/Documentation/git-send-email.txt
+++ b/Documentation/git-send-email.txt
@@ -450,6 +450,19 @@ edit ~/.gitconfig to specify your account settings:
 		smtpUser = yourname@gmail.com
 		smtpServerPort = 587
 
+If you have multifactor authentication setup on your gmail acocunt, you will
+need to generate an app-specific password for use with 'git send-email'. Visit
+https://security.google.com/settings/security/apppasswords to setup an
+app-specific password.  Once setup, you can store it with the credentials
+helper:
+
+	$ git credential fill
+	protocol=smtp
+	host=smtp.gmail.com
+	username=youname@gmail.com
+	password=app-password
+
+
 Once your commits are ready to be sent to the mailing list, run the
 following commands:
 
-- 
2.8.0