Adding doubling lines

[fehann]

Hello Hugo,

This is the first time I am doing a pull request, hope I am doing it correct. I added to the solution the reference lines that shows doubling rates. I was able to draw the lines but could not add the text in an automatic way, I had to tweak the position of the text until it was ok, so if there is any changes in the axis then it has to be reviewed.

I hope this helps, it was not easy for me to figure this one out.

Fernando

PS: I had to limit the plot to 5000 observations because it did not let me run more than that, it seems that Altair has a limit, not sure.