Update README.md

Author: developit

README.md

@@ -1,2 +1,11 @@
 # proptypes
-React's PropTypes, as a standalone module.
+
+> React's [PropTypes], packaged up as a standalone module.
+
+**DISCLAIMER:**
+This is literally copied from the React 0.14 codebase.
+If you're using PropTypes with React, it would be silly to reference this standalone version.
+
+**LICENSE:** BSD.
+
+[PropTypes]: https://github.com/facebook/react/blob/master/src/isomorphic/classic/types/ReactPropTypes.js