README: explain it's no coincidence the name is composite
freenode's #clusterlabs, 2017-11-09, times in CET:
> 17:11 * poki just prefers composites to abusing regular names like "racoon" :]
> 17:12 < poki> (assuming that clufter is highly composite as well)
Signed-off-by: Jan Pokorný <jpokorny@redhat.com>