Replace README boilerplate with a brief module description

Also note in DEPENDENCIES that this module requires Heimdal and uses
krb5-config, and will not work with MIT Kerberos.

README

 Heimdal/Kadm5 version 0.08
 ==========================
 
-The README is used to introduce the module and provide instructions on
-how to install the module, any machine dependencies it may have (for
-example C compilers and installed libraries) and any other information
-that should be provided before the module is installed.
-
-A README file is required for CPAN modules since CPAN extracts the
-README file from a module distribution so that people browsing the
-archive can use it get an idea of the modules uses. It is usually a
-good idea to provide version information here so that people can
-decide whether fixes for the module are worth downloading.
+Heimdal::Kadm5 is a Perl XS wrapper around the Heimdal Kerberos
+administrative client library (libkadm5clnt).  Heimdal is a free slightly
+less export challenged implementation of Kerberos5 by Assar Westerlund and
+Johan Danielsson.  This module exposes the API used to administer a
+Kerberos realm: add, remove, and list principals, create keytabs, change
+keys, and similar operations.
 
 INSTALLATION
 
@@ -23,13 +19,16 @@ To install this module type the following:
 
 DEPENDENCIES
 
-This module requires these other modules and libraries:
+This module requires the Kerberos administration client library for
+Heimdal (libkadm5clnt) and its corresponding header files.  It finds the
+path to the library and header files using krb5-config.
 
-  blah blah blah
+Only Heimdal is supported.  This module will not work with MIT Kerberos
+and its Kerberos administration client library, despite similarities in
+library and header file names.
 
 COPYRIGHT AND LICENCE
 
-
  Copyright (c) 2003, Stockholms Universitet
  (Stockholm University, Stockholm Sweden)
  All rights reserved.