Add fluid equations

docs/source/FluidEquations.rst

+Fluid Equations
+===============
+
+Below are the governing equations for the fluid:
+
+.. math:: \frac{\partial (\epsilon_g \rho_g)}{\partial t} + \nabla \cdot (\epsilon_g \rho_g U_g)  = 0
+  :label: eqn::mass_cons
+
+.. math:: \frac{ \partial (\epsilon_g \rho_g U)}{\partial t} + \nabla \cdot (\epsilon_g \rho_g U_g U_g) + \epsilon_g \nabla p_g = \nabla \cdot \tau + {\bf g}
+  :label: eqn::mom_cons
+
+.. math:: \frac{\partial \epsilon_g}{\partial t} + \nabla \cdot (\epsilon_g  U_g)  = 0
+  :label: eqn::mass_eps
+

docs/source/index.rst

@@ -22,7 +22,8 @@ the master branch at the beginning of each month.
 
    Introduction
    GettingStarted
-   Particle
+   FluidEquations
+   Particles
    ParticleBasics
    ParticleFluid
    ParticleWalls