add forge now : mention "reply all" in email to forge admin

in the email body of the add forge now forge admin template, add a mention to use "reply all" in order to male sure the answer will be automatically processed by the inbound system. (non blocking : in case of simple reply, the moderator will have to copy the message via the web UI moderation page, and change the request status to "feedback to handle")

Migrated from T4327 (view on Phabricator)

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information