add info about mypy usage to dev guide
@@ -23,6 +23,16 @@ without errors in non-strict mode. Using ``# type: ignore`` is fine in tricky
situations - type annotations should be helpful in understanding the code
and not be a burden.
+The following global options are required to pass `mypy`_ without error
+messages:
+
+.. code-block:: ini
+
+ [mypy]
+ python_version = 3.7
+ ignore_missing_imports = True
+ allow_redefinition = True
+
Design
------
