Add link to swift evolution mailing list

This should make it easier for new people to find the mailing list.

Author: cristeahub

README.md

@@ -1,6 +1,6 @@
 # Swift Programming Language Evolution
 
-**Before you initiate a pull request**, please read the process document. Ideas should be thoroughly discussed on the swift-evolution mailing list first.
+**Before you initiate a pull request**, please read the process document. Ideas should be thoroughly discussed on the [swift-evolution mailing list](https://swift.org/community/#swift-evolution) first.
 
 This repository tracks the ongoing evolution of Swift. It contains: