Suggestion: Add clarification on PRU_UART selection

[pra-dan]

Thanks for all your efforts. Just wanted to suggest that while discussing the PRU_UART (just as a mere debugging tool), mentioning the routing of PRU_software_UART (Tx) -> Hardware_UART (Rx) would be helpful.

Also, each PRU boasts 3 UARTs. The sample codes uart1.pru1_0.c and uart2.pru1_0.c don't specify how the software UARTs are selected (out of 3 per PRU), in the code.

Thanks