Add stepper driver docs

Author: glopesdev

.gitmodules

@@ -31,6 +31,9 @@
 [submodule "src/device.outputexpander"]
 	path = src/device.outputexpander
 	url = https://github.com/harp-tech/device.outputexpander.git
+[submodule "src/device.stepperdriver"]
+	path = src/device.stepperdriver
+	url = https://github.com/harp-tech/device.stepperdriver.git
 [submodule "protocol"]
 	path = protocol
 	url = https://github.com/harp-tech/protocol.git