Move images to img/ and update AddOns.md

Relocate image assets from DIY/img to a top-level img/ directory and add several new images. Update AddOns.md to use the new image paths, reorder and consolidate the Speedometer and GPS sections, clarify I2C wiring (recommend shielded twisted pair, shield->GND, and reduce SDA/SCL crosstalk), add guidance for relay-connected props with a relay module image, fix the splitter production link to the GitHub tree, and make minor wording/diagram label tweaks (decelleration -> deceleration). Files added: multiple img/*.jpg and img/*.png assets referenced by the updated document.

Author: CircuitSetup