jshn: fix missing usage for -p and -o arguments

Add missing usage hints for -p and -o arguments.

Fixes: e16fa068a573 ("jshn: add support for namespaces")
Fixes: eb30a03048f8 ("libubox, jshn: add option to write output to a file")
Signed-off-by: Petr Štetiar <ynezz@true.cz>

jshn.c

@@ -311,7 +311,7 @@ out:
 
 static int usage(const char *progname)
 {
-	fprintf(stderr, "Usage: %s [-n] [-i] -r <message>|-R <file>|-w\n", progname);
+	fprintf(stderr, "Usage: %s [-n] [-i] -r <message>|-R <file>|-o <file>|-p <prefix>|-w\n", progname);
 	return 2;
 }
 

tests/cram/test_jshn.t

@@ -6,7 +6,7 @@ set jshn for convenience:
 check usage:
 
   $ jshn
-  Usage: jshn [-n] [-i] -r <message>|-R <file>|-w
+  Usage: jshn [-n] [-i] -r <message>|-R <file>|-o <file>|-p <prefix>|-w
   [2]
 
 test bad json: