[FEATURE] Missing ~board config~ and Documentation about NuttX Boot Splashscreen

### Is your feature request related to a problem? Please describe.

Tim added support to NX Boot Splashscreen, but we still missing ~a board config example and~ a proper Documentation

### Describe the solution you'd like

- ~Create a board config~
- Create a documentation

### Describe alternatives you've considered

_No response_

### Verification

- [x] I have verified before submitting the report.