docs: add NationBuilder class docs

docs/index.rst

@@ -205,6 +205,7 @@ Indices and tables
    hustle
    mailchimp
    mobilize_america
+   nation_builder
    newmode
    ngpvan
    p2a

docs/nation_builder.rst

@@ -0,0 +1,52 @@
+NationBuilder
+==============
+
+********
+Overview
+********
+
+The NationBuilder class allows you to interact with the NationBuilder API. Users of this Parsons integration can download a full list of people, update and upsert people.
+
+.. note::
+  Authentication
+    In order to use this class you need your nation slug and access token. To get your access token login to your nation and navigate to ``Settings > Developer > API Token`` and create a new token. You can get more info in the `NationBuilder API docs <https://nationbuilder.com/api_quickstart>`_.
+
+==========
+Quickstart
+==========
+
+To instantiate the NationBuilder class, you can either store your ``NB_SLUG`` and ``NB_ACCESS_TOKEN`` keys as environment
+variables or pass them in as arguments:
+
+.. code-block:: python
+
+   from parsons import NationBuilder
+
+   # First approach: Use API key environment variables
+
+   # In bash, set your environment variables like so:
+   # export NB_SLUG='my-nation-slug'
+   # export NB_ACCESS_TOKEN='MY_ACCESS_TOKEN'
+   nb = NationBuilder()
+
+   # Second approach: Pass API keys as arguments
+   nb = NationBuilder(slug='my-nation-slug', access_token='MY_ACCESS_TOKEN')
+
+You can then make a request to get all people and save its data to a Parsons table using the method, ``get_people()``:
+
+.. code-block:: python
+
+    # Create Parsons table with people data from API
+    parsons_table = nb.get_people()
+
+    # Save people as CSV
+    parsons_table.to_csv('people.csv')
+
+The above example shows how to create a Parsons table with all people registered in your NationBuilder nation.
+
+***
+API
+***
+
+.. autoclass :: parsons.NationBuilder
+   :inherited-members: