Changed all headers in message to be the size of header 4 tags.

Made sure there is always a new line after code tag(```).

Change-Id: I772941a8bbf0634c9496ec648533110997e23cde
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1702293
Commit-Queue: Debrian Figueroa <debrian@google.com>
Reviewed-by: Robbie Iannucci <iannucci@chromium.org>