Update README.md

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README.md

@@ -2,7 +2,7 @@
 [![Homepage](https://img.shields.io/badge/Google_group-plumed--users-green.svg)](http://groups.google.com/forum/#!forum/plumed-users)
 [![License: LGPL v3](https://img.shields.io/badge/License-LGPL%20v3-blue.svg)](http://www.gnu.org/licenses/lgpl-3.0)
 [![Github Releases](https://img.shields.io/github/release/plumed/plumed2.svg)](https://github.com/plumed/plumed2/releases)
-[![Twitter Follow](https://img.shields.io/twitter/follow/plumed_org.svg?style=social&label=Follow)]()
+[![Twitter Follow](https://img.shields.io/twitter/follow/plumed_org.svg?style=social&label=Follow)](https://twitter.com/plumed_org)
 
 Branches and releases
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