PiSugar 3

**Is your feature request related to a problem? Please describe.**
N/A

**Describe the solution you'd like**
Documented battery module update

**Describe alternatives you've considered**
N/A

**Additional context**
The PiSugar 3 includes an RTC on the expansion board. Adding this to the documentation would be useful for people building a pwnagotchi for the first time as it would mean that a seperate RTC module does not need to be soldered.

The issue points to documentation for first-time Pwnagotchi builds and the PiSugar 3 RTC, but names no file or test. Start by locating the battery or RTC setup documentation and compare its current instructions with PiSugar 3. Done means the documentation explains that PiSugar 3 includes an RTC and that a separate RTC module is not needed.

Written by the indexing model from the issue text.