Linking to C library [gdc/mac]

[Graham MacDonald]

Apologies if this has been asked previously - I'm new to D and haven't 
seen the info anywhere.

I want to use a C library (glfw, probably others) from within my D code. 
  I want to link using gdc.  How can I do this?  Am I right in thinking 
I would have to create a D module (as described for dmd in 
http://www.digitalmars.com/d/htomodule.html)?

Thanks!

Graham