Fix discard instructions #409

This changes the text slightly to make it clearer what to best do with
the discard that's piling up when making the starter initially.

book/sourdough-starter/sourdough-starter.tex

@@ -234,11 +234,20 @@ \section{The process of making a starter}
 You will
 still have some mixture left from your first day. As this contains
 possibly dangerous pathogens that have been activated make sure you discard
-this mixture. Once your sourdough starter is mature you never need to
-discard it. It's long-fermented flour that is an excellent addon
+this mixture. A rule of thumb is to begin keeping the discard,
+the moment you made your first successful bread. At that point
+your discard is long-fermented flour that is an excellent addon
 used to make crackers, pancakes or delicious hearty sandwich
 bread\ldots I~also frequently dry it and use it as a rolling agent
-for pizzas that I~am making.
+for pizzas that I~am making \footnote{The discarding when making
+a new starter can be frustrating. As you proceed with bread-making
+you will hardly ever produce a lot of discard. You learn to make the
+exact amount of starter that you need to make bread dough. In fact
+you can also deplete all your starter and use a bit of bread dough
+as your next starter. If you have any discard left, it is a great
+use for other recipes, or as a source to revive your starter. I~typically
+store all my discard in one single jar in my fridge. Whenever I~have new
+discard I~just add it on top. Then I~proceed and use it whenever I~need.}.
 
 You should hopefully again see some bubbles, the starter increasing
 in size and/or the starter changing its smell. Some people give