Docs: Improve documentation on standard communication channels

More information about connection on IRC will hopefully help new
contributors.

README.md

@@ -33,12 +33,6 @@ regularly to indicate new official, stable release versions of Bitcoin Core.
 
 The contribution workflow is described in [CONTRIBUTING.md](CONTRIBUTING.md).
 
-The developer [mailing list](https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev)
-should be used to discuss complicated or controversial changes before working
-on a patch set.
-
-Developer IRC can be found on Freenode at #bitcoin-core-dev.
-
 Testing
 -------