description and instructions

README.md

 # N Body Simulation
 
+This code simulates particles under self-gravity. The forces are calculated via direct summation or with a tree and multipole expansion. 
+Most of the code is written in C++, Python is used to make plots and animations. OpenMP is used for parallelisation. 
 
+## Make build directory
 
+'''
+nbody$ mkdir build
+nbody$ cd build
+nbody/build$ cmake ..
+'''
 
-## Create Repository 
+## Compiling and running the simulation
 
-```
-git init
-git remote add origin git@gitlab.uzh.ch:armindamon.riess/nbody.git
-git pull --set-upstream origin master
-```
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+'''
+nbody/build$ make
+nbody/build$ ./nbody
+'''
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