imap-send: clarify CRAM-MD5 vs LOGIN documentation

Explicitly mention that leaving imap.authMethod unset makes
git imap-send use the basic IMAP plaintext LOGIN command.

Signed-off-by: Tony Finch <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: fanf2

Documentation/git-imap-send.txt

@@ -76,7 +76,8 @@ imap.preformattedHTML::
 
 imap.authMethod::
 	Specify authenticate method for authentication with IMAP server.
-	Current supported method is 'CRAM-MD5' only.
+	Current supported method is 'CRAM-MD5' only. If this is not set
+	then 'git imap-send' uses the basic IMAP plaintext LOGIN command.
 
 Examples
 ~~~~~~~~