README for libbsd

Due to the unusual layout of this package's libraries and headers it may be
required to set various build environment variables to allow other software
to discover libbsd, for example (alter as needed):

CFLAGS="${CFLAGS} -I/usr/opt/libbsd/include"
LDFLAGS="${LDFLAGS" -L/usr/opt/libbsd/lib"
LD_LIBRARY_PATH="/usr/oprt/libbsd/lib"
PKG_CONFIG_PATH="/usr/opt/libbsd/lib/pkgconfig"