docs(ot3): add documentation for the repl script (#10028)

api/src/opentrons/hardware_control/scripts/README.md

@@ -0,0 +1,18 @@
+# Hardware Control Scripts
+
+## Repl Script
+
+### Overview
+
+This script gives you access to a hardware controller object in a python shell. 
+
+### Running on an OT-3
+
+The script is installed to path by using the `make push-ot3` command. When you are ssh-ed in the robot, you can run `ot3repl` from anywhere.
+
+
+### Running on a computer
+
+Please review [the setup for a simulated CAN connection](https://github.com/Opentrons/opentrons/tree/edge/hardware#can-bus-simulation) to see how to run OT-3 simulators on your computer. Once you have a simulated CAN connection and firmware, you can run the following:
+
+`OPENTRONS_SIMULATION=true OT_API_FF_enableOT3HardwareController=true OT3_CAN_DRIVER_INTERFACE=opentrons_sock pipenv run python -m opentrons.hardware_control.scripts.repl`