Document format module.

doc/utils.md

@@ -138,6 +138,20 @@ Performs a reduce operation on the pairs of given dictionary using
 accept three arguments: the value accumulated so far, the key and the
 value.
 
+### Format
+
+    (import util-format)
+
+A simple module with less-common formatting functions.
+
+    (format-amount amt)
+
+* ```amt``` - a number
+
+Converts given number to a string with two-digit fractional
+part. Should the fractional part be 0, it is replaced with the string
+"--".
+
 ### IO
 
     (import util-io)