chore(README): update README

Update the mailing address

README.md

@@ -11,7 +11,7 @@ As a middleware toolkit, PowerAPI offers the capability of assembling power mete
 PowerAPI is an open-source project developed by the [Spirals research group](https://team.inria.fr/spirals) (University of Lille 1 and Inria) and fully managed with [sbt](http://www.scala-sbt.org/).
 
 ## Mailing list
-You can follow the latest news and asks questions by subscribing to our [mailing list](https://sympa.inria.fr/sympa/info/powerapi).
+You can follow the latest news and asks questions by subscribing to our <a href="mailto:sympa@inria.fr?subject=subscribe powerapi">mailing list</a>.
 
 ## Contributing
 If you would like to contribute code you can do so through GitHub by forking the repository and sending a pull request.