Update README with the style guide information

As decided in #24 let's follow tibbe's style for all new or modified
code.  Hopefully, with time, we'll end up with code that's a bit more
pleasant to read.

README.md

@@ -16,6 +16,8 @@ Transformation"](http://research.microsoft.com/en-us/um/people/simonpj/Papers/c-
 
 ### Development Notes
 
+#### Building and testing
+
 To build the library run:
 
     cabal configure
@@ -35,6 +37,12 @@ To run the tests with the test coverage report run:
 You'll need a Haskell Platform, which should include appropriate
 versions of Cabal and GHC.
 
+#### Coding style
+
+Please follow Johan Tibell's
+[Haskell Style Guide](https://github.com/tibbe/haskell-style-guide/blob/master/haskell-style.md)
+for all new/modified code.
+
 ### Checklist for Making Releases
 
 In order to facilitate GHC development's workflow, the version in [`hoopl.cabal`](hoopl.cabal) is to be bumped as soon as a change requires a respective version bump (according to the PVP) relative to the last released `hoopl` version.