Add description in addition to synopsis

I guess this is the only way to get no warning.

Author: Ericson2314

patch.cabal

@@ -1,6 +1,10 @@
 Name: patch
 Version: 0.0.0.1
-Description: Infrastructure for writing patches which act on other types.
+Synopsis: Infrastructure for writing patches which act on other types.
+Description:
+  In this library, a patch is something which can be applied, analogous to a
+  function, and which distinguishes returning the argument it was provided from
+  returning something else.
 License: BSD3
 License-file: LICENSE
 Author: Ryan Trinkle