add note to init tutorial

Author: hexaeder

docs/examples/init_tutorial.jl

@@ -61,15 +61,19 @@ end
 nothing #hide
 
 #=
-**B) A static prosumer node which forces a certain flow (pressure is fully implicit)**
+**B) A static prosumer node which forces a certain flow**
+
+!!! note "Fully Implicit Output"
+    We need to use `implicit_output(p)` to handle the fully implicit pressure
+    output. See [Fully Implicit Outputs](@ref) for details.
 =#
 @mtkmodel StaticProsumerNode begin
     @extend GasNode()
     @parameters begin
         q̃_prosumer, [description="flow injected by prosumer"]
     end
     @equations begin
-        -q̃_nw ~ q̃_prosumer
+        -q̃_nw ~ q̃_prosumer + implicit_output(p)
     end
 end
 nothing #hide