Update README.md

Author: clarus

README.md

@@ -1,13 +1,11 @@
 # ![Logo](https://raw.githubusercontent.com/clarus/icons/master/megaphone-48.png) IO
-[![Join the chat at https://gitter.im/clarus/io](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/clarus/io?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
-
-A library for effects in Coq.
+> A library for effects in Coq.
 
 ## Install
-Using OPAM for Coq:
+Using [OPAM for Coq](coq.io/opam/):
 
     opam repo add coq-released https://coq.inria.fr/opam/released
-    opam install coq:io
+    opam install coq-io
 
 ## Documentation
 See the complete documentation online on [v3.1.0](http://coq-io.github.io/doc/io/3.1.0/toc.html).