[Gimp-docs] Added dynamics

[Kolbjørn Stuestøl <kolbjoern stuestoel no>]

A few moments ago I added src/toolbox/paint/dynamics.xml to the 
gimp-help-2 repository.
This is a first sketch. Hoping someone will correct it, add new sections 
etc.
I have no drawing pad or something like that so it is impossible for me 
to write about using it.
Of course this is not the only way of describing the dynamics. Only 
meant as a start point. As usual: Feel free to make changes.
Kolbjoern