Update help to match behavior of inverter efficency cutoff

[brtietz]

Describe the bug

The current help description of the inverter efficiency cutoff suggests that it works all of the time. However, it only works for grid charging and discharging above the inverter DC limits.

To Reproduce

Steps to reproduce the behavior:

1. Create a case with a large inverter and a low critical load
2. Add a grid outage
3. See the battery discharging below the default 90% efficiency threshold

Expected behavior

The existing behavior might be what we want, but the help text should match the existing behavior

Screenshots

Code comments describing the behavior: