Add a link to the decimal module docs.

Doc/tut/tut.tex

@@ -5059,14 +5059,14 @@ want to run a full list sort:
 
 \section{Decimal Floating Point Arithmetic\label{decimal-fp}}
 
-The \module{decimal} module offers a \class{Decimal} datatype for
-decimal floating point arithmetic.  Compared to the built-in \class{float}
-implementation of binary floating point, the new class is especially
-helpful for financial applications and other uses which require exact
-decimal representation, control over precision, control over rounding
-to meet legal or regulatory requirements, tracking of significant
-decimal places, or for applications where the user expects the results
-to match hand calculations as taught in school.
+The \ulink{\module{decimal}}{../lib/module-decimal.html} module offers a
+\class{Decimal} datatype for decimal floating point arithmetic.  Compared to
+the built-in \class{float} implementation of binary floating point, the new
+class is especially helpful for financial applications and other uses which
+require exact decimal representation, control over precision, control over
+rounding to meet legal or regulatory requirements, tracking of significant
+decimal places, or for applications where the user expects the results to
+calculations done by hand.
 
 For example, calculating a 5\%{} tax on a 70 cent phone charge gives
 different results in decimal floating point and binary floating point.