improve documentation for security
improve documentation for security

Still not "secure by default", but at least all examples using a
session also use rack-protection and actually set a secret.
duykhoa/roda,johan--/roda,janko-m/roda,kematzy/roda,jeremyevans/roda,duykhoa/roda,janko-m/roda,anthonymiyoro/cuba,hilpitome/cuba,soveran/cuba,celsworth/roda,mikz/roda,kematzy/roda,jeremyevans/roda,soveran/cuba,jeremyevans/roda,kematzy/roda,johan--/roda,anthonymiyoro/cuba,mikz/roda,duykhoa/roda,janko-m/roda,Freaky/roda,mikz/roda,Freaky/roda,johan--/roda,hilpitome/cuba,celsworth/roda,celsworth/roda,Freaky/roda