Shrink and give example for sets question

[Vadim Zhukov]

Let's make it more informative and smaller size at the same time?

Index: install.sub
===================================================================
RCS file: /cvs/src/distrib/miniroot/install.sub,v
retrieving revision 1.958
diff -u -p -r1.958 install.sub
--- install.sub 24 Jan 2017 10:14:14 -0000      1.958
+++ install.sub 26 May 2017 15:49:08 -0000
@@ -1268,8 +1268,7 @@ select_sets() {
        cat <<__EOT
 
 Select sets by entering a set name, a file name pattern or 'all'. De-select
-sets by prepending a '-' to the set name, file name pattern or 'all'. Selected
-sets are labelled '[X]'.
+sets by prepending a '-', e.g.: '-x*'. Selected sets are labelled '[X]'.
 __EOT
        while :; do
                for _f in $_avail; do