fill out the readme a bit

README.markdown

@@ -0,0 +1,37 @@
+FakeFS
+======
+
+Mocha is great. But when your library is all about manipulating the
+filesystem, you really want to test the behavior and not the implementation.
+
+If you're mocking and stubbing every call to FileUtils or File, you're 
+tightly coupling your tests with the implementation.
+
+    def test_creates_directory
+      FileUtils.expects(:mkdir).with("directory").once
+      Library.add "directory"
+    end
+
+The above test will break if we decide to use `mkdir_p` in our code. Refactoring
+code shouldn't necessitate refactoring tests.
+
+With FakeFS:
+
+    def test_creates_directory
+      Library.add "directory"
+      assert File.directory?("directory")
+    end
+
+Woot.
+
+How is this different than MockFS?
+----------------------------------
+
+FakeFS provides a test suite and works with symlinks. It's also strictly a 
+test-time dependency: your actual library does not need to use or know about
+FakeFS.
+
+Authors
+-------
+
+Chris Wanstrath [chris@ozmm.org]