Allow %warning output to be suppressed

Allow the user to suppress user-specified warnings.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
diff --git a/doc/changes.src b/doc/changes.src
index 6624f12..b0f3ab4 100644
--- a/doc/changes.src
+++ b/doc/changes.src
@@ -13,6 +13,9 @@
 \b Make the behaviour of \c{-O0} match NASM 0.98 legacy behavior.
   See \k{opt-O}.
 
+\b \c{-w-user} can be used to suppress the output of \c{%warning} directives.
+  See \k{opt-w}.
+
 
 \S{cl-2.04} Version 2.04