Add a skeleton for architecture documentation

docs/html/development/architecture/index.rst

@@ -0,0 +1,20 @@
+===============================
+Architecture of pip's internals
+===============================
+
+.. note::
+    This section of the documentation is currently being written. pip
+    developers welcome your help to complete this documentation. If you're
+    interested in helping out, please let us know in the `tracking issue`_.
+
+.. note::
+    Direct use of pip's internals is *not supported*.
+    For more details, see :ref:`Using pip from your program`.
+
+
+.. toctree::
+    :maxdepth: 2
+
+
+
+.. _`tracking issue`: https://github.com/pypa/pip/issues/6831

docs/html/development/index.rst

@@ -14,6 +14,7 @@ or the `pypa-dev mailing list`_, to ask questions or get involved.
 
     getting-started
     contributing
+    architecture/index
     release-process
     vendoring-policy