Add package level docs

doc.go

@@ -0,0 +1,18 @@
+// Copyright 2016 The CMux Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+// implied. See the License for the specific language governing
+// permissions and limitations under the License.
+
+// Package cmux is a library to multiplex network connections based on
+// their payload. Using cmux, you can serve different protocols from the
+// same listener.
+package cmux