docs: README for transports (TCP/UDP/Auto/Multicast) and udp:// slots #75

Follow-up to #70, #72, #73, to do once they and the README refresh (#66) are merged, so the READMEs (EN/RU/ZH) are edited once:

• The per-slot transport in the URL dialog: TCP (default), UDP, Auto (UDP with fallback to TCP), Multicast (RTSP multicast with fallback to TCP, Android 8+). What each is for; that OpenIPC cameras do not do RTSP multicast (RTSP multicast and other RTSP transports (research: Majestic RTSP has no multicast) #69).
• udp:// slots for Majestic outgoing: URL forms (udp://@:5600, udp://@239.1.2.3:5600, udp://source@group:port, ?codec=/&pt=), how to set the destination on the camera, PT 96/97.
• The transport extra of the share intent.
• Facts confirmed by the device round in Device testing: UDP, plain RTP and RTSP multicast (#70, #72, #73) #74 (e.g. whether Majestic sends to a multicast group).