Added a helpful template script for running Astaroth simulations.

This is has been personally helpful in practical use.

scripts/my_cmake.sh

@@ -0,0 +1,20 @@
+#!/bin/bash
+
+# This is a sample script. Please copy it to the directory you want to run the
+# code in and customize occordingly. 
+
+# The following write the commit indentifier corresponding to the simulation
+# run  into a file. This is to help keep track what version of the code was
+# used to perform the simulation.
+
+git rev-parse HEAD > COMMIT_CODE.log 
+
+# Run cmake to construct makefiles
+# In the case you compile in astaroth/build/ directory. Otherwise change ".." to
+# the correct path to astaroth/CMakeLists.txt
+
+cmake -DDOUBLE_PRECISION=ON -DDSL_MODULE_DIR=acc/mhd_solver ..
+
+# Standard compilation
+
+make -j