Since after the release a lot of downstream users will not be building
from source, it makes a lot more sense to have an option to fall back to
the Xinerama extension for those that are still on systems that do not
support RandR.
Replace the dependency list in the README to mention libxrandr instead
of libxinerama since that's the default value of the MULTIMON variable
in config.mk
Remove xext and xft as a dependency since they are not currently used
and probably haven't been used a while.
Also remove freetype2 from the pkg-config list, while it is required by
pangocairo it should be included from the pkg-config --cflags call.
Move README to docs/dunst.pod to be used as man page. Write a README with building instructions and dependencies. Remove INSTALL as it's no longer necessary.
