xfstests: update README file to document some recent changes

Update the README file to document the new _cat_passwd and
_cat_group functions, and to recommend passing "-n" to
getfacl(1) so it produces numeric output.

Signed-off-by: Alex Elder <aelder@sgi.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>

README

@@ -160,6 +160,20 @@ Test script environment:
 				  string DATE for deterministic
 				  output
 
+	_cat_passwd,		- dump the content of the password
+	_cat_group		  or group file (both the local file
+				  and the content of the NIS database
+				  if it is likely to be present)
+
+     4. General recommendations, usage conventions, etc.:
+	- When the content of the password or group file is
+	  required, get it using the _cat_passwd and _cat_group
+	  functions, to ensure NIS information is included if NIS
+	  is active.
+	- When calling getfacl in a test, pass the "-n" argument so
+	  that numeric rather than symbolic identifiers are used in
+	  the output.
+
 Verified output:
 
     Each test script has a numerical name, e.g. 007, and an associated