I'm looking for an english, ideally relatively modern reference for the fact that the outer automorphism group of $SL(2,\mathbb{F}_p)$ is order $2$ (for $p$ odd), generated by conjugation by an element of $GL(2,\mathbb{F}_p)$ of nonsquare determinant.
Other references would also be nice.
If anyone has a nice looking pdf of Dieudonne's "La geometrie des groupes classiques" that would be nice as well. I can only find a poorly scanned djvu version.
One place where what you are asking about appears explicitly is Robert Wilson's book "The Finite Simple Groups", page 50: