Udpate stiff starter instructions (#72)

Some people reported the dough was too dry. This can happen if the flour
used absorbs more water. Every flour has a unique water absorption
capacity.

book/sourdough-starter/sourdough-starter-types.tex

@@ -184,7 +184,10 @@ times to make lacto-fermented hot sauces.
 
 The stiff starter is the driest of all the starters. It has a hydration of
 around 50 to 60 percent. So for 100 grams of flour you are using around 50 to
-60 grams of water.
+60 grams of water. If you can't mix flour and water because the
+mixture is too try you need to increase the water quantity. This is often
+the case when using whole wheat flour to make your starter. The stiff
+starter should have the consistency of pasta or pizza dough.
 
 \begin{figure}[!htb]
   \includegraphics{figures/fig-stiff-starter-conversion.pdf}