Update documentation.

doc.go

diff --git a/doc.go b/doc.go
index f3ea1fe..a11d46b 100644
--- a/doc.go
+++ b/doc.go
@@ -2,13 +2,34 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// goproperties provides functions for reading and writing
-// Java properties files and has support for Spring like
-// property expansion.
+// goproperties provides functions for reading
+// ISO-8859-1 (Java) and UTF-8 encoded .properties files and has
+// support for Spring-like property expansion.
 //
-// By default, if a value contains a reference '${key}' then
-// getting the value will recursively expand the key to its value.
-// The format is configurable and circular references are not allowed.
+//   key = value
+//   # key2 = value
+//   key2 = ${key}
+//
+// The default property expansion format is ${key} but can be
+// changed by setting different pre- and postfix values on the
+// Properties object.
+//
+//   p := goproperties.NewProperties()
+//   p.Prefix = "#["
+//   p.Postfix = "]#"
+//
+// Property expansion is recursive and circular references are not allowed.
+// If a circular reference is detected an error is logged and the
+// unexpanded value is returned.
+//
+//   # Circular reference
+//   key = ${key}
+//
+//   # Malformed expression
+//   key = ${ke
+//
+// When writing properties to a writer currently only ISO-8859-1 encoding
+// is supported.
 //
 // See one of the following links for a description of the properties
 // file format.