Link to docs

Link to docs from the top level README.

Fixes #13

Author: Khionu Sybiern

README.md

@@ -1,3 +1,5 @@
 # tcpproxy
 
-See https://godoc.org/github.com/google/tcpproxy/
+For library usage, see https://godoc.org/github.com/google/tcpproxy/
+
+For CLI usage, see https://github.com/google/tcpproxy/blob/master/cmd/tlsrouter/README.md