Add portability note and reference to the platform hints FAQ answer

tests/README

@@ -5,6 +5,14 @@ verify basic functionality of the LDAP libraries, slapd, and slurpd.
 	To run BDB tests, type "make bdb".
 	To run LDBM tests, type "make ldbm".
 
+The test scripts depends on a number of tools commonly available on
+Unix (and Unix-like) systems.  While attempts have been made to make
+these scripts reasonable portable, they may not run properly on your
+system.  You may have to adjust your path so that compatible versions
+of tools used are available to the scripts and/or you may have to
+install replacement tools.  Platform specific hints may be found at:
+	http://www.openldap.org/faq/index.cgi?file=9
+
 To modify the debug level the tests run slapd with, set the SLAPD_DEBUG
 environment variable.
 	env SLAPD_DEBUG=1 make test