add info about Server#verification_level
add info about Server#verification_level

megumisonoda/discordrb,VxJasonxV/discordrb,megumisonoda/discordrb,Roughsketch/discordrb,meew0/discordrb,VxJasonxV/discordrb,Roughsketch/discordrb,meew0/discordrb