Create running-example.md

Author: TimGoTheCreator

docs/running-example.md

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+# Running a example in NEXT
+
+To run a example in NEXT, you need to *cd* to an example path
+You aswell need a python interpeter
+For this, lets try the ColdCollapseGalaxy
+```bash
+cd examples
+cd ColdCollapseGalaxy
+python coldcollapse.py
+../../next coldcollapse.txt 8 0.25 0.2 vtu
+```
+
+Explaining the flags:
+../../next = Go up 2 directories (into project root) and run executable
+coldcollapse.txt = The name of the specified "scenario" / "initial condition"
+8 = Set openmp threads to 8, if your cpu has more, you can change it
+0.25 = Timestep, how fast the simulation will run
+0.2 = Caching interval, how fast NEXT would plot caching
+vtu = Caching format, there is aswell vtk