README.md mistake

[beyoung]

import quadkey

# qk = quadkey.from_geo((-105, 40), 17)  
# the order of lng and lat is incorrect  
# the right order should be as follow
quadkey.from_geo(( 40, -105), 17)

print qk.key # => 02310101232121212 
assert qk.level is 17
tile = qk.to_tile() # => [(x, y), z]