README.md: added screenshots

README.md

doc/images/janus-camera-full-screen-20201226-135814.png

doc/images/novnc-camera-full-screen-20201226-140345.png

doc/images/novnc-desktop-20201226-135635.png

...images/novnc-desktop-and-janus-camera-20201226-135830.png

doc/images/novnc-desktop-janus-camera-20201226-180026.png

...desktop-janus-camera-and-novnc-camera-20201226-140423.png

...mages/novnc-om-board-and-janus-camera-20201226-135905.png

...m-board-janus-camera-and-novnc-camera-20201226-140306.png

doc/images/novnc-welcome-screen-20201226-135612.png

doc/images/pult-channel-1-20201226-153714.png

doc/images/pult-channel-6-20201226-154050.png

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doc/images/pult-starting-om-board-20201226-135845.png

doc/images/pult-starting-vnc-20201226-135607.png

doc/images/pult-vnc-and-camera-started-20201226-135647.png