FAQ for shifting the boundaries of PlotEquiMap

Hi @rfernand and @aho!

First of all, I have created a new section FAQ on s2dv package, following the structure of startR. Please, An-Chi, let me know if you can think in a better way to include this kind of information for users.

@rfernand, could you look to its content, run the code and correct it or make any suggestion you consider necessary?

Thanks to all!

Núria