only support building with GNU Make
only support building with GNU Make

Update the documentation to state that openrc only works with gnu make.
This needs to be done in order to address the parallel build issue.

X-Gentoo-Bug: 289264
X-Gentoo-Bug-URL: http://bugs.gentoo.org/show_bug.cgi?id=289264

dwfreed/openrc,williamh/openrc,williamh/openrc,OpenRC/openrc,dwfreed/openrc,williamh/openrc,dwfreed/openrc,OpenRC/openrc,OpenRC/openrc