Add a Diff output format

shellcheck.1.md

@@ -152,6 +152,23 @@ not warn at all, as `ksh` supports decimals in arithmetic contexts.
           ...
         </checkstyle>
 
+**diff**
+
+:   Auto-fixes in unified diff format. Can be piped to `git apply` or `patch -p1`
+    to automatically apply fixes.
+
+    --- a/test.sh
+    +++ b/test.sh
+    @@ -2,6 +2,6 @@
+     ## Example of a broken script.
+     for f in $(ls *.m3u)
+     do
+    -  grep -qi hq.*mp3 $f \
+    +  grep -qi hq.*mp3 "$f" \
+	 && echo -e 'Playlist $f contains a HQ file in mp3 format'
+     done
+
+
 **json1**
 
 :   Json is a popular serialization format that is more suitable for web