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: NRich Salz <rsalz@openssl.org>

doc/dir-locals.example.el

+;;; This is an example of what a .dir-locals.el suitable for OpenSSL
+;;; development could look like.
+;;;
+;;; Apart from setting the CC mode style to "OpenSSL-II", it also
+;;; makes sure that tabs are never used for indentation in any file,
+;;; and that the fill column is 78.
+;;;
+;;; For more information see (info "(emacs) Directory Variables")
+
+((nil
+  (indent-tabs-mode . nil)
+  (fill-column . 78)
+  ;; (auto-fill-mode . t)  ;; optional.
+  )
+ (c-mode
+  (auto-fill-mode . nil)   ;; auto-fill makes more harm than good in C
+  (c-file-style . "OpenSSL-II")))

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.
 
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