Happy Hare Warning

More of a suggestion to update the Binky readme.md to mention that ERCF_CALIBRATE_ENCODER will likely generate a warning that can be ignored if using happy hare v1 software:

`Warning: Encoder is not detecting the expected number of counts. It is possible that reflections from some teeth are unreliable`

This can be worked around by editing the ercf.py file, but also seems safe to just ignore.