Update README.md

Added link to Niklas Hammerstone´s work

README.md

@@ -1,7 +1,10 @@
 # OPAL
 
 Minimalistic FW for Processing GCode commands to xy2-100 protocol and control periferal devices.
-The default usecase is a 3D printer/engraver.
+The default usecase is a 3D printer/engraver. Galvos driven by XY2-100 protocol are refered to as Digital Galvos and are
+the subject of this repo.. Other options are Analog Galvos like the RC1001 and the various "Lasershow galvos" sold on e-bay.
+Analog galvos are not covered here but might have their own section in the future. The last option is Steppermotor driven
+galvos. More info on this can be found in GalvoStep here:  https://github.com/NiklasHammerstone/GalvoStep
 
 If you are using the software please join: https://www.reddit.com/r/OpenGalvo/ and write a comment or share your project!