docs: replace http to https

README.md

@@ -19,7 +19,7 @@ of the Tor bandwidth authorities, to avoid creating unnecessary traffic.
 
 **ADVICE**: It is recommended to read this documentation at
 [Read the Docs](https://sbws.rtfd.io). In
-[Github](http://github.com/torproject/sbws) some links won't be properly
+[Github](https://github.com/torproject/sbws) some links won't be properly
 rendered.
 It can also be read after installing the Debian package ``sbws-doc`` in
 ``/usr/share/doc/sbws`` or after building it locally as explained in