add grid lines (major) to chart.

There are commented out lines of code to display the 'minor' grid lines along side the 'major' additions.

light-wave.py

@@ -24,7 +24,11 @@ plt.xlabel("<---    Oldest (Time) Latest    --->")
 plt.ylabel("Light")
 plt.legend(loc='lower left')
 ax.set_xticklabels(())
+ax.grid(b=True, linestyle='dashdot', which='major', color='grey', linewidth=0.5)
 
+# Minor grid marks -- uncomment to display
+# ax.grid(b=True, linestyle='dashdot', which='minor', color='grey', linewidth=0.5)
+# plt.minorticks_on()
 
 # Updates the line chart for factory1
 def animate1(i, ys):