zgrep: usage should say which grep options are not supported

* zgrep.in (usage): Document which grep options are not supported.
Problem reported by Liron Paryente in
<http://lists.gnu.org/archive/html/bug-grep/2013-06/msg00005.html>.

diff --git a/zgrep.in b/zgrep.in
index 154d17f4cea73a20179fdcb86a014fc670a9a465..c149577c57b417994d791a744037366e4eba4a65 100644 (file)
--- a/zgrep.in
+++ b/zgrep.in
@@ -42,7 +42,10 @@ usage="Usage: $0 [OPTION]... [-e] PATTERN [FILE]...
 Look for instances of PATTERN in the input FILEs, using their
 uncompressed contents if they are compressed.
 
-OPTIONs are the same as for 'grep'.
+OPTIONs are the same as for 'grep', except that the following 'grep'
+options are not supported: --dereference-recursive (-R), --directories (-d),
+--exclude, --exclude-from, --exclude-dir, --include, --null (-Z),
+--null-data (-z), and --recursive (-r).
 
 Report bugs to <bug-gzip@gnu.org>."