Create README.md

Create g-code from a heightmap image.

Features:
- Compensate for tool size for square-ended and ball-ended milling bits
- Skip over pixels that are 100% white (value of 255), to mask off areas that won't be cut
- Choose your cutting path
   - X or Y direction
   - Climb or conventional milling, or alternating rows
- Removal of extraneous g-code
   - Take out X,Y,Z values when they are the same as the last line
   - Remove coordinates that are in a straight line between the previous and next coordinates