caucase-stack: Inform about importing with context

Context, nicely filled in by slapos.recipe.template, is required in the macros.

stack/caucase/README.rst

@@ -12,6 +12,10 @@ into your software release.
 server components of caucase.
 
 
+Remember, that importing the template has to happen with context:
+
+``{{ import "caucase" as caucase with context }}``
+
 Software
 --------