add support for frienclycore-20.04

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check setqt5env

rk3399: update opencv to 4.2.0

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Update README.md

Update README.md

Update README.md

Correct device detection

Improve usb camera priority

Firmware released after 20190830, the index of the camera device name needs to be increased by 1.

update README.md

Update README.md

Update README.md

Update README.md