Add .editorconfig to prevent whitespace conflicts

Some IDE support this out of the box, others will need a plugin.
For more details see https://EditorConfig.org

.editorconfig

@@ -0,0 +1,15 @@
+# EditorConfig for YACReader
+# see https://EditorConfig.org
+
+root = true
+
+[*]
+charset = utf-8
+trim_trailing_whitespace = true
+end_of_line = lf
+insert_final_newline = true
+indent_style = space
+indent_size = 4
+
+[*.yml]
+indent_size = 2