Add a link to the discussion forums.

Author: hyanwong

advanced_msprime.md

@@ -20,4 +20,7 @@ do some particular things with it. This chapter is broken down into the followin
 sections:
 
 ```{tableofcontents}
-```
+```
+
+For discussion of other advanced msprime topics, you might also want to look at
+the [msprime discussion forums](https://github.com/tskit-dev/msprime/discussions).