add EditorConfig

.editorconfig

@@ -0,0 +1,16 @@
+# EditorConfig is awesome: http://EditorConfig.org
+
+# top-most EditorConfig file
+root = true
+
+# Space indentation
+[*]
+indent_style = space
+indent_size = 2
+trim_trailing_whitespace = true
+
+# The indent size used in the `package.json` file cannot be changed
+# https://github.com/npm/npm/pull/3180#issuecomment-16336516
+[{*.yml,*.yaml,package.json}]
+indent_style = space
+indent_size = 2