Add simple EditorConfig

The EditorConfig file applies the formatting rules described in CONTRIBUTING.md.

.editorconfig

@@ -0,0 +1,10 @@
+# EditorConfig: http://editorconfig.org/
+
+root = true
+
+[*.java]
+charset = utf-8
+indent_style = space
+indent_size = 4
+trim_trailing_whitespace = true
+insert_final_newline = true