Advertise --validate-utf8 in usage information

This option was added in 04726a7 (Added `CMARK_OPT_VALIDATE_UTF8`
option. - 2015-06-16) but not "documented".

1 files changed, 1 insertions, 0 deletions

diff --git a/src/main.c b/src/main.c
index 9482f68..8942520 100644
--- a/src/main.c
+++ b/src/main.c
@@ -32,6 +32,7 @@ void print_usage() {
   printf("  --nobreaks       Render soft line breaks as spaces\n");
   printf("  --safe           Suppress raw HTML and dangerous URLs\n");
   printf("  --smart          Use smart punctuation\n");
+  printf("  --validate-utf8  Replace UTF-8 invalid sequences with U+FFFD\n");
   printf("  --help, -h       Print usage information\n");
   printf("  --version        Print version\n");
 }