I'm sure this must be an obvious thing but a quick Google didn't tell me. How can I add a message to G-Code that will be displayed when running the code? I want to do a machine stop for a manual tool change and it would be nice for it to remind me what tool and what RPM to use.

Mach3 has a little text prompt where it gives errors and tells you when it is in E-Stop etc.. I assume text can be made to display here from the code.