Add minimal example to readme.md

User feedback suggests that adding a minimal (6-7) line example just underneath the introduction of tagplot and publish would be useful

fig = figure;
plot(x,y);
[fig, IDs] = PlotID.TagPlot(fig);
script = [mfilename('fullpath'),'.m'];
rdata =  {'\\fullpath\dataset01.mat', '\\fullpath\dataset02.h5'} ;
PlotID.Publish(rdata, script, fig);