[docs] stub out kernel doc

docs/structure/kernel.rst

@@ -4,16 +4,43 @@ kernel
 The ``kernel`` module provides submodules for handling global resources
 and services. It's designed around some explicit goals:
 
+-  Any function or object that can modify global state must be contained
+   in this module for easy search/grepability. ``using nwk = nw::kernel`` is an acceptable abreviation.
 -  Every service should be easily overrideable to allow for `parallel
    implementation <http://sevangelatos.com/john-carmack-on-parallel-implementations/>`__.
 -  Every service should be decoupled from the kernel itself.
--  Any function or object that can modify global state must be contained
-   in this module for easy search/grepability.
+
+Config
+~~~~~~
+
+:cpp:struct:`nw::kernel::Config`
 
 Services
 --------
 
-Config
-~~~~~~
+EffectSystem
+------------
+
+EventSystem
+-----------
+
+FactionSystem
+-------------
+
+ModelCache
+----------
+
+ObjectSystem
+------------
+
+Rules
+-----
+
+Strings
+-------
+
+TilesetRegistry
+---------------
 
-The ``Config`` service provides access to installation info.
+TwoDACache
+----------