add notes about scons/swig
add notes about scons/swig

Noctem/pogeo,micolous/s2-geometry-library,laramiel/s2-geometry-library,Noctem/pogeo,laramiel/s2-geometry-library,yjwong/s2-geometry-library,yjwong/s2-geometry-library,yjwong/s2-geometry-library,micolous/s2-geometry-library,Noctem/pogeo,Noctem/pogeo,micolous/s2-geometry-library,yjwong/s2-geometry-library,laramiel/s2-geometry-library,micolous/s2-geometry-library