DOCS: Add snaplog command documentation.

Author: kareltucek

doc-dev/other/troubleshooting_c2usb.md

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+# How to gather logs from uhk whose usb doesn't work
+
+Put this into a macro named `$onInit`:
+
+```
+zephyr uhk logs 1
+zephyr log enable wrn Battery
+zephyr log enable wrn Bt
+zephyr log enable wrn StateSync
+zephyr log enable inf udc
+zephyr log enable wrn udc_nrf
+zephyr log enable inf hogp
+zephyr log enable dbg c2usb
+```
+
+Adjust log levels as needed. 
+
+You can see the logs in real time:
+
+- on the oled display
+- in Agent's advanced settings (click the Agent button 7x on the about page and scroll up)
+
+Create this macro and bind it somewhere convenient:
+
+```
+zephyr uhk snaplog
+```
+
+Reproduce the issue. 
+
+Run the `snaplog` macro. This will export the usb log buffer into the persistent status buffer.
+
+Restart uhk using its reset button
+
+Start Agent. 
+
+Yellow bar should pop up with the zephyr your log.