proposal/custom-type-errors.md

@@ -4,6 +4,9 @@
 This page outlines the design for a GHC feature to provide support for user-specified type errors.
 The main idea was presented by Lennart Augustsson at the 2015 Haskell Symposium in Vancouver BC. 
 
+
+The relevant ticket is [\#9637](https://gitlab.haskell.org//ghc/ghc/issues/9637).
+
 ### The Problem