Add readme for custom monitoring script

examples/monitor_serial_hexbytes/README.md

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+# Custom serial port monitoring script `hexbytes`
+This folder contains a Python module which can be imported by the DIP Testbed Client `hardware-serial-monitor` command.  
+
+Module contents:
+- `mock.py` - Mocks of all DIP Testbed related Python classes needed to implement a custom monitoring solution,
+  this is added for doing type checking in IDEs.
+- `monitor.py` - The actual monitoring script, which exports a `monitor` variable containing the monitoring class with a method `run`
+
+The monitoring script gets run with an instance of `socketlike: Socketlike`, which allows receiving/transmitting monitoring messages to/from the backend.  
+
+This specific `hexbytes` implementation is a copy-paste of the original `hardware-serial-monitor` monitoring type `hexbytes`, simply implemented as an external script/module.  
+
+This script does the following:
+- receives bytes from the `socketlike`, formats and prints them out to `STDOUT`  
+- captures/supresses `STDIN` from printing to `STDOUT`  
+- redirects all `STDIN` bytes to transmit through `socketlike`  
+- on error conditions or exit signals reverts the capture of `STDIN`, closes the `socketlike` connection, returns an exit result