update ReadMe to include SFCGAL and preferred versions of GEOS/GDAL/CGAL.  Put pretty anchors in install so doesn't create hard to bookmark numbered anchors.

git-svn-id: http://svn.osgeo.org/postgis/trunk@11413 b70326c6-7e19-0410-871a-916f4a2858ee
repeat create extension instructions in short -- heck its shorter than the crap we have listed. Also correect compile instructions (with-raster and -with-topology no longer need stating) get rid of other obsolete statements

git-svn-id: http://svn.osgeo.org/postgis/trunk@11414 b70326c6-7e19-0410-871a-916f4a2858ee
missed one comment

git-svn-id: http://svn.osgeo.org/postgis/trunk@11415 b70326c6-7e19-0410-871a-916f4a2858ee