comment on disabled warnings

_CoqProject

 -Q theories iris_examples
--arg -w -arg -notation-overridden,-redundant-canonical-projection,-several-object-files,-convert_concl_no_check
+# We sometimes want to locally override notation (e.g. in proofmode/base.v, bi/embedding.v), and there
+# is no good way to do that with scopes.
+-arg -w -arg -notation-overridden
+# non-canonical projections (https://github.com/coq/coq/pull/10076) do not exist yet in 8.9.
+-arg -w -arg -redundant-canonical-projection
+# change_no_check does not exist yet in 8.9.
+-arg -w -arg -convert_concl_no_check
+# "Declare Scope" does not exist yet in 8.9.
+-arg -w -arg -undeclared-scope
+
 theories/barrier/proof.v
 theories/barrier/specification.v
 theories/barrier/barrier.v