Add note about vertical alignment to patch guidelines.

git-svn-id: file:///var/local/repositories/ffmpeg/trunk@9695 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

doc/ffmpeg-doc.texi

@@ -1749,6 +1749,9 @@ do not attach several unrelated patches to the same mail.
 @item
     You should maintain alphabetical order in alphabetically ordered lists as
     long as doing so does not break API/ABI compatibility.
+@item
+    Lines with similar content should be aligned vertically when doing so
+    improves readability.
 @item
     Did you provide a suggestion for a clear commit log message?
 @end enumerate