doc: mention Java version 8 is required
doc: mention Java version 8 is required

Ref: #3543

jitsi/jitsi-meet,gpolitis/jitsi-meet,gpolitis/jitsi-meet,jitsi/jitsi-meet,bgrozev/jitsi-meet,bgrozev/jitsi-meet,gpolitis/jitsi-meet,jitsi/jitsi-meet,jitsi/jitsi-meet,bgrozev/jitsi-meet,jitsi/jitsi-meet,gpolitis/jitsi-meet,bgrozev/jitsi-meet,gpolitis/jitsi-meet,gpolitis/jitsi-meet,gpolitis/jitsi-meet,bgrozev/jitsi-meet,bgrozev/jitsi-meet,gpolitis/jitsi-meet,jitsi/jitsi-meet,jitsi/jitsi-meet,jitsi/jitsi-meet