Proposal: Create Developer_Cookbook.md

docs/Developer_Cookbook.md

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+# Developer Cookbook
+How to do common tasks within the Kalico.
+
+## Moving the Toolhead
+First get the toolhead object:
+```
+toolhead = self.printer.lookup_object("toolhead")
+```
+The toolhead object is not always available at module initalization time so it
+should be looked up at time of use.
+
+All moves with the toolhead are absolute moves. However you can instruct the
+toolhead not to move an axis by passing `None` for a coordinate to
+`manual_move()`. E.g this will move the toolhead to z=10mm at its current
+x/y position:
+```
+toolhead.manual_move([None, None, 10.], speed)
+```
+
+To make a relative move, use the current toolhead position. This will lift
+the Z axis by 10mm:
+```
+pos = toolhead.get_position()
+toolhead.manual_move([None, None, pos[2] + 10.], speed)
+```