python-netifaces: fix license file name

License info is stored in README.rst, not README.

[Peter: reword]
Signed-off-by: David Graziano <david.graziano@rockwellcollins.com>
Signed-off-by: Clayton Shotwell <clayton.shotwell@rockwellcollins.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>