ADD api document on line

app/docs/slate/.editorconfig

@@ -0,0 +1,18 @@
+# EditorConfig is awesome: https://EditorConfig.org
+
+# Top-most EditorConfig file
+root = true
+
+# Unix-style newlines with a newline ending every file
+[*]
+end_of_line = lf
+insert_final_newline = true
+indent_style = space
+indent_size = 2
+trim_trailing_whitespace = true
+
+[*.rb]
+charset = utf-8
+
+[*.md]
+trim_trailing_whitespace = false