README.md : Experiments with adding images.

README.md

 `python plot_seq.py ~/temp/p_ac_3_od/60 p_ac.yml 12`
 
 
-![Multi Plot 1](doc/multi_plot.svg)
+![Multi Plot 1](doc/multi_plot.png)
 
 plot_seq.py `do_td_multi_plot(inDir,cfg.analysisArgs,[(36,4), (48,2)] )`