Docs/rewrite how watch works in english

동사가 다른걸 제가 못봤네요. 여튼, Unwatch button으로 바꿔서 수정하겠습니다.

If a user click the Unwatch button on an object, Yobi removes the user from "Explicit Watchers" list of the object and adds the user to the list of "Explicit Ignorers". It works even if the user does not have permission to read the object.