[qty.sym.expr.algo] Add article "the"

docs/api_reference/src/quantities.tex

@@ -1243,7 +1243,7 @@
 \end{itemdescr}
 
 \pnum
-\exposid{expr-map} maps contents of one symbolic expression to another resulting in a different type list.
+\exposid{expr-map} maps the contents of one symbolic expression to another resulting in a different type list.
 
 \indexlibraryglobalexpos{expr-map}
 \begin{itemdecl}