Because even the best software ever is nothing without a proper documentation, writing a proper decent one was my first priority when I officialy took the maintenance of phpGraphy.
As an experienced computer's user, I generally only read the first three lines of a documentation and then run the software directly and learn by using it, but sometime when it's either a complex software or if I really want to know all the tricks that I could use with a software, then the documentation is my reference. I've too often see nice softwares with a poor documentation ! So I hope you'll find this document useful either as a starting point or as a reference book. I've tried all along the writing to keep it easy to read and accessible even for non IT specialists but a minimum basis is somehow required !.