Add mypy doc (#1611)

content/en/docs/instrumentation/python/mypy.md

@@ -0,0 +1,33 @@
+---
+title: Using mypy
+---
+
+If you're using [mypy](http://mypy-lang.org/), you'll need to turn on [namespace
+packages](https://mypy.readthedocs.io/en/stable/command_line.html#cmdoption-mypy-namespace-packages),
+otherwise `mypy` won't be able to run correctly.
+
+To turn on namespace packages, do one of the following:
+
+Add the following to your project configuration file:
+
+```toml
+[tool.mypy]
+namespace_packages = true
+```
+
+Or, use a command-line switch:
+
+```shell
+mypy --namespace-packages
+```
+
+## Using the `strict` option
+
+If you're using the `strict` option with mypy, and you're using the
+OpenTelemetry Python SDK (instead of just the API), you'll need to also set the
+following in your project configuration file:
+
+```toml
+[mypy-opentelemetry.sdk.*]
+implicit_reexport = True
+```