[CODING_STYLE] Add vim modeline

Add my vim recipe that most closely matches the coding style. If you can
improve it, please do so!

CODING_STYLE

@@ -269,9 +269,23 @@ In general, be wary of performing any arithmetic operations in an
 argument to malloc.  You should explicitly check for integer overflow
 yourself in any more complex situations.
 
+Mode lines
+----------
+
+So given the rules above, what is the best way to simplify one's life as
+a code monkey? Get your editor to do most of the tedious work of
+beautifying your code!
+
+As a reward for reading this far, here are some mode lines for the more
+popular editors:
+/*
+ * vim:sw=4:sts=4:ts=8:tw=78:fo=tcroq:cindent:cino=\:0,(0
+ * vim:isk=a-z,A-Z,48-57,_,.,-,>
+ */
+
 
 TODO
 ----
 
 Write rules for common editors to use this style.  Also cleanup/unify
-the modlines in the source files.
+the modelines in the source files.