Add editorconfig with 4 spaces in general and 2 spaces in xml

This is how it is described in the readme

.editorconfig

@@ -0,0 +1,18 @@
+# EditorConfig helps developers define and maintain
+# consistent coding styles between different editors and IDEs.
+
+root = true
+
+[*]
+end_of_line = lf
+charset = utf-8
+trim_trailing_whitespace = true
+insert_final_newline = true
+indent_style = space
+indent_size = 4
+
+[*.xml]
+indent_size = 2
+
+[*.md]
+trim_trailing_whitespace = false