add some basic info

documentation/_static/overview.rst

 Overview and Tutorial
 =====================
 
-At the moment, this code is meant to run pseudospectral DNS of
-Navier-Stokes, using FFTW 3, and to integrate particle trajectories in
-the resulting fields.
-I'm trying to write it as general as possible, so that it can be
-expanded in the future; it remains to be seen how well this will work.
-
-The Navier-Stokes solver has been extensively tested (tests are included
-in the repository), and it is working as expected. Parameters and
-statistics are stored in HDF5 format, together with code information,
-so simulation data should be "future proof".
-
-Users of this code are expected to either use `NavierStokes` objects
-directly, or construct their own class that inherits this class.
-The way I use it is to I inherit and add custom statistics as necessary; I
-also have private C++ code that can get added and used when needed.
-I plan on adding documentation on the procedure as when other people
-show interest in using the code, or when time permits.
+Equations
+---------
 
+The code uses a fairly standard pseudo-spectral algorithm to solve fluid
+equations.
+The incompressible Navier Stokes equations in velocity form are as
+follows:
+
+.. math::
+
+    \partial_t \mathbf{u} + \mathbf{u} \cdot \nabla \mathbf{u} =
+    - \nabla p + \nu \Delta \mathbf{u} + \mathbf{f}
+
+In fact, the code solves the vorticity formulation of these equations:
+
+.. math::
+    \partial_t \mathbf{\omega} +
+    \mathbf{u} \cdot \nabla \mathbf{\omega} =
+    \mathbf{\omega} \cdot \nabla \mathbf{u} +
+    \nu \Delta \mathbf{\omega} + \nabla \times \mathbf{f}
+
+Tutorial
+--------
 

documentation/index.rst

@@ -3,6 +3,7 @@
    You can adapt this file completely to your liking, but it should at least
    contain the root `toctree` directive.
 
+
 Welcome to bfps's documentation!
 ================================
 
@@ -14,7 +15,6 @@ Welcome to bfps's documentation!
    /_static/development
 
 
-
 Indices and tables
 ==================