Add an example .dir-locals.el

This file, when copied to .dir-locals.el in the OpenSSL source top,
will make sure that the CC mode style "OpenSSL-II" will be used for
all C files.

Additionally, I makes sure that tabs are never used as indentation
character, regardless of the emacs mode, and that the fill column is
78.

Reviewed-by: Rich Salz <rsalz@openssl.org>

doc/openssl-c-indent.el

@@ -21,6 +21,8 @@
 ;;;
 ;;; A new buffer with .dir-locals.el will appear.  Save it (C-x C-s).
 ;;;
+;;; Alternatively, have a look at dir-locals.example.el
+
 ;;; For suggesting improvements, please send e-mail to levitte@openssl.org.
 
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;