bpo-11681: Document the `-b` and `-bb` options (GH-1562)

diff --git a/Modules/main.c b/Modules/main.c
index 73e87e0..a6edf82 100644
--- a/Modules/main.c
+++ b/Modules/main.c
@@ -62,6 +62,8 @@
 /* Long usage message, split into parts < 512 bytes */
 static char *usage_1 = "\
 Options and arguments (and corresponding environment variables):\n\
+-b     : issue warnings about comparing bytearray with unicode\n\
+         (-bb: issue errors)\n\
 -B     : don't write .py[co] files on import; also PYTHONDONTWRITEBYTECODE=x\n\
 -c cmd : program passed in as string (terminates option list)\n\
 -d     : debug output from parser; also PYTHONDEBUG=x\n\