Fixed README.[rst->md] path in MANIFEST.in.
Fixed README.[rst->md] path in MANIFEST.in.

Signed-off-by: Brett Randall <3a817d01b0aca4da51b95766d5e85950536c2c6e@gmail.com>

postmanlabs/httpbin,kennethreitz/httpbin,kennethreitz/httpbin,postmanlabs/httpbin,krissman/httpbin,Runscope/httpbin,Runscope/httpbin,krissman/httpbin,ewdurbin/httpbin,ewdurbin/httpbin