Be clearer about what 'low' means

[fatuhoku]

Thanks for putting RRFPSBar together! It's really going to help me gauge the scrolling performance of my collection view cells.

It took me a while to figure out that the FPS being plotted on the bar was in fact the rolling time series / data points, and that the low figure was the minimum FPS for that time series, and avg was the average over that whole time series.

The average FPS isn't really that useful unless it's over a shorter amount of time, like 3 seconds.

[RolandasRazma]

any suggestions? :)