Add a .dir-locals.el

That's basically project-level configuration for Emacs users. As I keep my
fill-column set to 80 by default, it's useful for me to change it here.

.dir-locals.el

@@ -0,0 +1,12 @@
+;;; Directory Local Variables
+;;; For more information see (info "(emacs) Directory Variables")
+
+((ruby-mode
+  (bug-reference-url-format . "https://github.com/rubocop-hq/rubocop/issues/%s")
+  (bug-reference-bug-regexp . "#\\(?2:[[:digit:]]+\\)")
+  (indent-tabs-mode . nil)
+  (fill-column . 100)))
+
+;; To use the bug-reference stuff, do:
+;;     (add-hook 'text-mode-hook #'bug-reference-mode)
+;;     (add-hook 'prog-mode-hook #'bug-reference-prog-mode)