Add docstring style to contribution code style guide (Netflix#1328)

* Add docstring style to contribution code style guide

* Move code style guide from README to CONTRIBUTING.md

* Replace link to Sphinx with nbdoc

* Trigger Build

Author: InterferencePattern

CONTRIBUTING.md

@@ -14,3 +14,9 @@ Everyone is welcome to join us in our [chatroom](http://chat.metaflow.org)!
 Please maintain appropriate, professional conduct while participating in our community. This includes all channels of
 communication. We take reports of harassment or unwelcoming behavior very seriously. To report such behavior, please 
 contact us via [email](mailto:[email protected]). 
+
+### Code style
+
+We use [black](https://black.readthedocs.io/en/stable/) as a code formatter. The easiest way to ensure your commits are always formatted with the correct version of `black` it is to use [pre-commit](https://pre-commit.com/): install it and then run `pre-commit install` once in your local copy of the repo.
+
+We also follow the [numpydoc](https://numpydoc.readthedocs.io/en/latest/format.html) docstring style to enable automatic documentation using [nbdoc](https://github.com/outerbounds/nbdoc).

README.md

@@ -48,8 +48,3 @@ There are several ways to get in touch with us:
 ## Contributing
 
 We welcome contributions to Metaflow. Please see our [contribution guide](https://docs.metaflow.org/introduction/contributing-to-metaflow) for more details.
-
-### Code style
-
-We use [black](https://black.readthedocs.io/en/stable/) as a code formatter. The easiest way to ensure your commits are always formatted with the correct version of `black` it is to use [pre-commit](https://pre-commit.com/): install it and then run `pre-commit install` once in your local copy of the repo.
-