Adding outline for the usage documentation.

Author: pacesm

docs/index.rst

@@ -18,6 +18,7 @@
   :caption: Package Documentation
 
   Installation <installation>
+  Usage <usage>
   License <license>
 
 ..   Module Reference <api/modules>

docs/usage.rst

@@ -0,0 +1,53 @@
+Usage
+=====
+
+WIP
+
+Magnetic Models
+---------------
+
+- how to load and evaluate magnetic models
+- generic model interface
+- core and lithospheric models
+- magnetospheric models
+- ionospheric models
+- combined and composed models
+- field line tracing
+
+Coordinate Conversions
+----------------------
+- magnetic coordinates
+    - Quasi-Dipole coordinates (with and without the base vectors)
+    - Magnetic Local Time
+    - dipole coordinates
+    - magnetic universal time
+- geographic coordinates
+    - spherical coordinates
+    - Cartesian coordinates
+    - geodetic (WGS84) coordinates
+- vector rotations between different coordinate frames
+
+Time Conversions
+----------------
+- MJD2000 <=> decimal year
+- MDD2000 => year fraction
+
+Sun Positions
+-------------
+
+- ``sunpos``
+
+Utilities
+---------
+
+- vector operations
+
+Low Level Spherical Harmonics
+-----------------------------
+- ``legendre``
+- ``loncossin``
+- ``relradpow``
+- ``sheval``
+- ``sheval_dipole``
+- ``sphargrd``
+- ``spharpot``