docs: correct Lovelace card entity IDs in README

Hybrid PV sensors are named PV Voltage/Current/Power N (not DC *),
the total is Total PV Power, the status text sensor is Status String,
and the TOU switch is Time of Use. Also fix the pv2_current typo and
document device-based entity ID naming above the examples.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: fboundy