Begin adding user-facing documentation

Especially around invocation and configuration

docs/source/user/configuration.rst

@@ -0,0 +1,29 @@
+====================
+ Configuring Flake8
+====================
+
+Once you have learned how to :ref:`invoke <invocation>` Flake8, you will soon
+want to learn how to configure it so you do not have to specify the same
+options every time you use it.
+
+This section will show you how to make
+
+.. prompt:: bash
+
+    flake8
+
+Remember that you want to specify certain options without writing
+
+.. prompt:: bash
+
+    flake8 --select E123,W456 --enable-extensions H111
+
+
+Configuration Locations
+=======================
+
+Presently, Flake8 supports storing its configuration in the following places:
+
+- Your top-level user directory
+
+- In your project in one of ``setup.cfg``, ``tox.ini``, or ``.flake8``.