Changelog entry for removing reducers library

As b8586de is an internal change
which may affect some users (those using TemplateFunction to define
black boxes) it should have a changelog entry so it can be included
in the release notes later.

changelog/2021-06-01T09_44_12+02_00_remove_reducers.md

@@ -0,0 +1 @@
+CHANGED: clash-lib now uses Data.Monoid.Ap instead of Data.Semigroup.Monad.Mon. This means users defining primitives with TemplateFunction will need to replace Mon/getMon with Ap/getAp.