C Axis as Second Spindle

I am looking for guidance on how to setup the C axis as a second spindle.  This is for a rose engine lathe (otbok.info/index.php?n=Main.RoseEngineLathe) where we need to use:

1. the Spindle to rotate the piece, and
2. the C axis to rotate the rosettes used to impart the design

We turn these quite slowly, certainly less than 10 RPM, and at times speeds approaching 3 or 4 minutes per revolution.  Thusly we are using stepper motors for both axes.

The end goal is to drive the spindle and the C axis simultaneously, but specifying a relationship percentage for their rotational speeds.  For example,  Is there some documentation I can read which describes 

1. How to setup LinuxCNC to treat the C-axis as a secondary spindle, and
2. The G-code I would use.

Apologies if this is already been asked and answered:  I searched the forum and could not find it.

I did not realize that was there. I will look into it. Thank you.