Add instructions for installing the Python module to the README.
Add instructions for installing the Python module to the README.

Bruce rightly ran into the situation where he hadn't done so, and things failed in non-obvious ways.
srenatus/dxr,jay-z007/dxr,KiemVM/Mozilla--dxr,bozzmob/dxr,kleintom/dxr,bozzmob/dxr,kleintom/dxr,kleintom/dxr,gartung/dxr,pombredanne/dxr,jay-z007/dxr,jay-z007/dxr,jonasfj/dxr,gartung/dxr,bozzmob/dxr,bozzmob/dxr,KiemVM/Mozilla--dxr,pelmers/dxr,pombredanne/dxr,pelmers/dxr,gartung/dxr,pombredanne/dxr,nrc/dxr,pelmers/dxr,pelmers/dxr,bozzmob/dxr,erikrose/dxr,jbradberry/dxr,jonasfj/dxr,srenatus/dxr,jbradberry/dxr,jbradberry/dxr,jay-z007/dxr,gartung/dxr,nrc/dxr,erikrose/dxr,KiemVM/Mozilla--dxr,gartung/dxr,jay-z007/dxr,erikrose/dxr,jay-z007/dxr,jbradberry/dxr,nrc/dxr,bozzmob/dxr,jonasfj/dxr,srenatus/dxr,nrc/dxr,kleintom/dxr,KiemVM/Mozilla--dxr,KiemVM/Mozilla--dxr,jonasfj/dxr,jonasfj/dxr,jbradberry/dxr,pombredanne/dxr,gartung/dxr,pelmers/dxr,nrc/dxr,gartung/dxr,bozzmob/dxr,erikrose/dxr,pelmers/dxr,jonasfj/dxr,nrc/dxr,pombredanne/dxr,srenatus/dxr,jbradberry/dxr,kleintom/dxr,jbradberry/dxr,pombredanne/dxr,KiemVM/Mozilla--dxr,srenatus/dxr,pelmers/dxr,pombredanne/dxr,jay-z007/dxr,kleintom/dxr,erikrose/dxr,kleintom/dxr,srenatus/dxr