Add .editorconfig file. (#301)

diff --git a/.editorconfig b/.editorconfig
new file mode 100644
index 0000000..bdc3756
--- /dev/null
+++ b/.editorconfig
@@ -0,0 +1,12 @@
+root = true
+
+[*]
+charset = utf-8
+trim_trailing_whitespace = true
+end_of_line = lf
+indent_style = space
+indent_size = 4
+insert_final_newline = true
+
+[*.yml]
+indent_size = 2