Set HTML indent size in editorconfig to 4

This is matching djhtml's default indent size and much easier to read.

.editorconfig

@@ -9,6 +9,9 @@ indent_style = space
 insert_final_newline = true
 trim_trailing_whitespace = true
 
+[*.html]
+indent_size = 4
+
 [*.py]
 indent_size = 4
 max_line_length = 119