add readme for sims

code/simulations/readme_sim.md

+Simulation code (Matlab R2020a) 
+
+Figure2.m reproduces Fig. 2 and (optionally) supplementary Fig. S1.
+Requires Parallel Computing Toolbox
+Figure appearance adjusted for 27" (2560 x 1440) display
+
+Qmovie(x) plays supplementary Movie M1 with a delay of x seconds
+Movie appearance adjusted for 13" (2560 x 1600) laptop display
+
+For questions, or if you spot any errors, please contact spitzer@mpib-berlin.mpg.de 
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