doc: Add OpenSSH pub certkey auth.
doc: Add OpenSSH pub certkey auth.

wangshawn/libssh,rofl0r/libssh,DouglasHeriot/libssh,taikoo/libssh,mwgoldsmith/ssh,nviennot/libssh,nviennot/libssh,bigcat26/libssh-mod,DouglasHeriot/libssh,bigcat26/libssh-mod,Distrotech/libssh,jt1/honeypot-libssh,Distrotech/libssh,sebadoom/libssh,pouete/libssh,mwgoldsmith/ssh,DouglasHeriot/libssh,kedazo/libssh,Distrotech/libssh,nviennot/libssh,mwgoldsmith/libssh,robxu9/libssh,robxu9/libssh,rofl0r/libssh,bigcat26/libssh-mod,mwgoldsmith/ssh,mwgoldsmith/libssh,rofl0r/libssh,pouete/libssh,jt1/honeypot-libssh,sebadoom/libssh,kedazo/libssh,elastichosts/libssh,elastichosts/libssh,sebadoom/libssh,kedazo/libssh,sebadoom/libssh,jt1/honeypot-libssh,wangshawn/libssh,bigcat26/libssh-mod,Distrotech/libssh,taikoo/libssh,taikoo/libssh,robxu9/libssh,robxu9/libssh,rofl0r/libssh,nviennot/libssh,pouete/libssh,wangshawn/libssh,mwgoldsmith/libssh,taikoo/libssh,wangshawn/libssh,mwgoldsmith/ssh,mwgoldsmith/libssh,elastichosts/libssh,kedazo/libssh,DouglasHeriot/libssh,jt1/honeypot-libssh,pouete/libssh