Add documentation on how to display received frames, view transmitted frames.

Author: aentinger

libraries/Arduino_CAN/extras/scripts/README.md

@@ -6,3 +6,11 @@ This directory contains helpful shell scripts when working with CAN.
 ```bash
 sudo ./setup_scan.sh
 ```
+Display received CAN frames via [`candump`](https://manpages.ubuntu.com/manpages/jammy/man1/candump.1.html):
+```bash
+candump can0
+```
+Transmit CAN frames via [`cansend`](https://manpages.ubuntu.com/manpages/jammy/man1/cansend.1.html):
+```bash
+cansend can0 00001234#DEADBEEF
+```