Remove old communication methods from README
Neither the email address nor the twitter account are actively used
these days.
* [Raise a bug / request an enhancement](https://github.com/cocotb/cocotb/issues/new) (Requires a GitHub account)
* [Join the mailing list](https://lists.librecores.org/listinfo/cocotb)
* [Join the Gitter chat room](https://gitter.im/cocotb)
-* Get in contact: [E-mail us](mailto:cocotb@potentialventures.com)
-* Follow us on twitter: [@PVCocotb](https://twitter.com/PVCocotb)
## Installation
