Add better Thunderbird information.
Add Thunderbird Registry instructions to:
  Enable UTF8 & Preformat mode
  Disable HTML mode
Signed-off-by: NPaul McQuade <paulmcquad@gmail.com>
Signed-off-by: NRandy Dunlap <rdunlap@xenotime.net>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>