Fixes [YOCTO #11107]
Updated the SSTATE_MIRRORS variable description to include
explanation of how to use regular expressions to map file locations
to server-provided URLs to share sstate information.
(From yocto-docs rev: 1357095864ee919f576de8df36f4e177b24fdd22)
Signed-off-by: Scott Rifenbark <srifenbark@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>