File README_OBS_BUILD of Package klayout

BUILD FAILURES:

* Fedora no longer includes libruby-static.a in their ruby-devel package
   - and no "-static" package exists.  As the code uses rb_vm_top_self
  (to call the embedded ruby interpreter), the build fails.
  Note: libruby.so does not contain this function. For Red Hat/Fedora,
  see also https://bugzilla.redhat.com/show_bug.cgi?id=428384