ot_rcp example could use more documentation and debug steps (IDFGH-14378)

[stevenlybeck]

Answers checklist.

• I have read the documentation ESP-IDF Programming Guide and the issue is not addressed there.
• I have updated my IDF branch (master or release) to the latest version and checked that the issue is present there.
• I have searched the issue tracker for a similar issue and not found a similar issue.

General issue report

I'm attempting to use openthread daemon for the Host portion of an openthread co-processor design - along with an esp32-c6 flashed with the ot_rcp firmware.

There aren't really any comprehensive instructions about this, but I'm finding that ot-daemon bails as it attempts to connect to my esp32 devboard flashed with ot_rcp:

>> sudo ./build/posix/src/posix/ot-daemon --verbose 'spinel+hdlc+uart:///dev/cu.usbmodem101?uart-baudrate=460800&no-reset'
Jan  8 00:11:00  ./build/posix/src/posix/ot-daemon[49362] <Info>: Running OPENTHREAD/thread-reference-20230706-1115-gdc4acf034-dirty; POSIX; Jan  7 2025 23:50:16
Jan  8 00:11:00  ./build/posix/src/posix/ot-daemon[49362] <Info>: Thread version: 5
Jan  8 00:11:04  ./build/posix/src/posix/ot-daemon[49362] <Critical>: 49d.21:57:21.396 [C] Platform------: Init() at spinel_driver.cpp:83: Failure

I realize this is a kind of cross-project issue - but my hope is that espressif can provide more comprehensive guidance on using ot_rcp specifically for Thread (and Zigbee) Sniffing.