doc: Improve the PKI documentation a bit.
doc: Improve the PKI documentation a bit.

pouete/libssh,bigcat26/libssh-mod,kedazo/libssh,mwgoldsmith/libssh,DouglasHeriot/libssh,wangshawn/libssh,Distrotech/libssh,mwgoldsmith/libssh,mwgoldsmith/ssh,Distrotech/libssh,mwgoldsmith/ssh,taikoo/libssh,Distrotech/libssh,mwgoldsmith/ssh,sebadoom/libssh,elastichosts/libssh,Distrotech/libssh,sebadoom/libssh,elastichosts/libssh,kedazo/libssh,kedazo/libssh,DouglasHeriot/libssh,taikoo/libssh,wangshawn/libssh,nviennot/libssh,DouglasHeriot/libssh,bigcat26/libssh-mod,mwgoldsmith/ssh,robxu9/libssh,sebadoom/libssh,mwgoldsmith/libssh,robxu9/libssh,elastichosts/libssh,bigcat26/libssh-mod,nviennot/libssh,wangshawn/libssh,kedazo/libssh,pouete/libssh,nviennot/libssh,taikoo/libssh,robxu9/libssh,wangshawn/libssh,pouete/libssh,DouglasHeriot/libssh,pouete/libssh,sebadoom/libssh,nviennot/libssh,mwgoldsmith/libssh,robxu9/libssh,bigcat26/libssh-mod,taikoo/libssh