add comment in _CoqProject

_CoqProject

@@ -7,7 +7,7 @@
 # Custom flags (to be kept in sync with the dune file at the root of the repo).
 # Fixing this one requires Coq 8.19
 -arg -w -arg -argument-scope-delimiter
-# https://gitlab.mpi-sws.org/iris/stdpp/-/issues/216
+# Warning seems incorrect, see https://gitlab.mpi-sws.org/iris/stdpp/-/issues/216
 -arg -w -arg -notation-incompatible-prefix
 
 stdpp/options.v