Fix DynamicPPL import

Author: penelopeysm

developers/compiler/model-manual/index.qmd

@@ -28,6 +28,8 @@ However, models can be constructed by hand without the use of a macro.
 Taking the `gdemo` model above as an example, the macro-based definition can be implemented also (a bit less generally) with the macro-free version
 
 ```{julia}
+using DynamicPPL
+
 # Create the model function.
 function gdemo2(model, varinfo, context, x)
     # Assume s² has an InverseGamma distribution.