add additional properties to editorconfig - ref slimphp/Slim#2457

Author: danopz

.editorconfig

@@ -2,7 +2,12 @@
 root = true
 
 [*]
+charset = utf-8
+insert_final_newline = true
 end_of_line = lf
 indent_style = space
 indent_size = 4
-trim_trailing_whitespace = true
+trim_trailing_whitespace = true
+
+[*.md]
+trim_trailing_whitespace = false