* subversion/libsvn_ra_serf/README: Clarify how to enable ra_serf.
* subversion/libsvn_ra_serf/README: Clarify how to enable ra_serf.

Found by: Charles Acknin <charlesacknin@gmail.com>

jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion