[recipes] Add a comment about recipe fields

[Matthias Clasen <matthiasc src gnome org>]

commit 97c22cfe917caa75c139bc41f5f009035c1a90b4
Author: Matthias Clasen <mclasen redhat com>
Date:   Thu Mar 9 12:01:52 2017 -0500

    Add a comment about recipe fields
    
    This just caused two bugs that I needed to fix.

 src/gr-recipe.c |   10 ++++++++++
 1 files changed, 10 insertions(+), 0 deletions(-)
---
diff --git a/src/gr-recipe.c b/src/gr-recipe.c
index d991a21..eed4f64 100644
--- a/src/gr-recipe.c
+++ b/src/gr-recipe.c
@@ -31,6 +31,16 @@
 #include "gr-app.h"
 #include "types.h"
 
+/* Note:
+ *
+ *  If any fields are added to a recipe, there are several places
+ *  that need to be kept in sync:
+ *  - save_recipes() in gr-recipe-store.c
+ *  - load_recipes() in gr-recipe-store.c
+ *  - the GrRecipeExporter code
+ *  - the GrRecipeImporter code
+ */
+
 struct _GrRecipe
 {
         GObject parent_instance;