Push discussion of API key to the end. (#253)

docs/intro.rst

@@ -23,23 +23,6 @@ or `poetry <https://python-poetry.org/>`_ to manage
 your dependencies, then you can add ``censusdis`` the
 same way you would add any other dependency.
 
-Census API Key (Optional Initially)
------------------------------------
-
-The Census API that ``censusdis`` calls requires the use of an API
-key unless you are doing only a relatively small number of queries.
-Luckily, the key is free and easy to get, and once you have one in
-a file in the right place on your machine ``censusdis`` will automatically
-use it with every call to the Census API.
-
-To obtain a key, visit `this page <https://api.census.gov/data/key_signup.html>`_.
-The key will be sent to you be email. It will be a long string of numbers 
-and letters. Make a directory called ``.censusdis`` in your home directory,
-then inside that directory create a text file called ``api_key.txt``. The file
-should have just one line, and you should paste the key you got via email
-into it. Once this is done, all ``censusdis`` calls to the Census API will
-use this key.
-
 Making Your First Query
 -----------------------
 
@@ -566,6 +549,29 @@ There are additional more advanced examples and
 additional maps and visualizations,
 presented in more `Demo Notebooks <./notebooks.html>`_.
 
+Census API Key (Optional Initially)
+-----------------------------------
+
+The Census API that ``censusdis`` calls recommends the use of an API
+key. But chances are you were able to make it through all of the examples
+above without one. This is because
+until you are doing a large number of queries, you don't need
+one. But
+once you are doing a large number of queries or putting `censusdis` into
+a production pipeline, you should return to this section and obtain a key.
+
+Luckily, the key is free and easy to get, and once you have a key in
+a file in the right place on your machine ``censusdis`` will automatically
+use it with every call to the Census API.
+
+To obtain a key, visit `this page <https://api.census.gov/data/key_signup.html>`_.
+The key will be sent to you be email. It will be a long string of numbers
+and letters. Make a directory called ``.censusdis`` in your home directory,
+then inside that directory create a text file called ``api_key.txt``. The file
+should have just one line, and you should paste the key you got via email
+into it. Once this is done, all ``censusdis`` calls to the Census API will
+use this key.
+
 Help and Issues
 ---------------