Add EditorConfig configuration

http://editorconfig.org allows you to have a single source of
configuration for *lots* of source code editors, which means that,
upon everyone using them, all noise on commits will be gone, as
everyone will be using the same formatting style for files.

docs/contribute/conventions.rst

@@ -105,6 +105,30 @@ style on ZCML <http://docs.zope.org/zopetoolkit/codingstyle/zcml-style.html>`_
   between attributes and nested elements.
 
 
+EditorConfig
+------------
+
+`EditorConfig <http://editorconfig.org/>`_
+provides a way to share the same configuration for all major source code editors.
+
+You only need to install the plugin for your editor of choice,
+and add the following configuration on ``~/.editorconfig``.
+
+.. sourcecode:: ini
+
+    [*]
+    indent_style = space
+    end_of_line = lf
+    insert_final_newline = true
+    trim_trailing_whitespace = true
+    charset = utf-8
+
+    [*.py]
+    indent_size = 4
+
+    [{*.html,*.dtml,*.pt,*.zpt,*.xml,*.zcml,*.js}]
+    indent_size = 2
+
 Quoting
 =======