Add some text to configure on how to install dependencies with yum.

Add some text on how to install dependencies with yum for Fedora or
other systems that use yum for package management.  Since the named of
the required packages on Fedora are slightly different from Debian
this will help get new users of notmuch that use Fedora going quicker.

Signed-off-by: Jeffrey C. Ollie <jeff@ocjtech.us>