Add support for function-recipes

pangeo_forge_runner/commands/bake.py

@@ -262,7 +262,7 @@ def start(self):
 
                 # if pangeo-forge-recipes is <=0.9, we have to specify a requirements.txt
                 # file even if it isn't present, as the image used otherwise will not have pangeo-forge-recipes
-                if isinstance(recipe, PTransform):
+                if isinstance(recipe, PTransform) or inspect.isfunction(recipe):
                     requirements_path = feedstock.feedstock_dir / "requirements.txt"
                     if requirements_path.exists():
                         extra_options["requirements_file"] = str(requirements_path)