Add baker's math chapter

This adds the start of the making a starter chapter by introducing
the concept of baker's math

book/book.tex

@@ -7,6 +7,7 @@
 \usepackage{booktabs}
 \usepackage{filecontents}
 \usepackage{longtable}
+\usepackage{float}
 \usepackage[T1]{fontenc}
 \usepackage{tocloft}
 \usepackage[backend=biber]{biblatex}
@@ -63,12 +64,7 @@
 \input{basics/how-sourdough-works}
 
 \chapter{Making a sourdough starter}
-\section{Baker's math}
-\section{The process of making a starter}
-\section{How flour is fermented}
-\section{Determining starter readiness}
-\section{Maintenance}
-\section{Longterm starter storage}
+\input{sourdough-starter/sourdough-starter}
 
 \chapter{Sourdough starter types}
 \section{The regular starter}