Added minor information about the difference between gadget-2 and minimal

doc/RTD/source/HydroSchemes/minimal_sph.rst

@@ -12,7 +12,8 @@ Minimal (Density-Energy) SPH
 This scheme is a textbook implementation of Density-Energy SPH, and can be used
 as a pedagogical example. It also implements a Monaghan AV scheme, like the
 GADGET-2 scheme. It uses very similar equations, but differs in implementation
-details. To use the minimal scheme, use
+details; namely it tracks the internal energy \(u\) as the thermodynamic
+variable, rather than entropy \(A\). To use the minimal scheme, use
 
 .. code-block:: bash