rc-status: improve usage message accuracy and consistency

This makes it more clear that many of the options are used as an
alternative to a runlevel.

Signed-off-by: Andrew Gregory <andrew.gregory.8@gmail.com>

src/rc/rc-status.c

@@ -172,7 +172,9 @@ print_services(const char *runlevel, RC_STRINGLIST *svcs)
 }
 
 #include "_usage.h"
-#define extraopts "[runlevel1] [runlevel2] ..."
+#define usagestring ""						\
+	"Usage: rc-status [options] <runlevel>...\n"		\
+	"   or: rc-status [options] [-a | -c | -l | -r | -s | -u]"
 #define getoptstring "aclrsu" getoptstring_COMMON
 static const struct option longopts[] = {
 	{"all",         0, NULL, 'a'},