DOC: Update README to fix broken links.

Author: carterbox

README.rst

@@ -32,9 +32,9 @@ Contribute
 ==========
 
 * Issue Tracker: https://github.com/tomography/xdesign/issues
-* Documentation: https://github.com/tomography/xdesign/tree/master/doc
+* Documentation: https://github.com/tomography/xdesign/tree/master/docs
 * Source Code: https://github.com/tomography/xdesign/tree/master/xdesign
-* Tests: https://github.com/tomography/xdesign/tree/master/test
+* Tests: https://github.com/tomography/xdesign/tree/master/tests
 
 License
 =======