Added end_of_line & some more info about this file

> It is acceptable and often preferred to leave certain EditorConfig properties unspecified. For example [...] if a property is not standardized in your project (end_of_line for example), it may be best to leave it blank.

http://editorconfig.org/#file-format-details

I added ``end_of_line`` nonetheless, as I think there is an agreement to always use ``lf``.

.editorconfig

@@ -1,4 +1,5 @@
-# editorconfig.org
+; This file is for unifying the coding style for different editors and IDEs.
+; More information at http://editorconfig.org
 
 root = true
 
@@ -6,6 +7,7 @@ root = true
 charset = utf-8
 indent_size = 4
 indent_style = space
+end_of_line = lf
 insert_final_newline = true
 trim_trailing_whitespace = true