Your English is not bad at all. It is excellent! I wasn't really clear. I lump coherency/consistency changes all in with "grammar/spelling", even though the two aren't really related. They're all just minor edits that may make the tutorial polished, e.g. consistent capitalization/periods, clarification, or w/e. I don't think I really need to change the spelling or grammar in your case since it is already well done. But I do that with every tutorial that I approve, so it isn't something to worry about.