Added how to configure with the minimal hydro scheme to the docs

doc/RTD/source/HydroSchemes/minimal_sph.rst

@@ -12,4 +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.
+details. To use the minimal scheme, use
+
+.. code-block:: bash
+
+    ./configure --with-hydro="minimal"