Documentation lacks info about EXIF handling

# Expected Behavior

Documentation includes EXIF handling:

- how can EXIF be accessed
- how to PRESERVE or copy EXIF to`.clone()` instance
- how to add new EXIF data, if no EXIF was set / is in the image
- how to manipulate existing EXIF data
- how to EXIF-Auto-Rotate (I believe I read somewhere about this)
- is anyhing besides EXIF supported?

# Current Behavior

Documentatin is missing info about EXIF.

# Failure Information (for bugs)

none.

## Steps to Reproduce

Read the `readme.md`

## Context

- Jimp Version: 0.16.1
- Operating System: OSX /Win latest
- Node version: 15.11.0

## Failure Logs

none.