The MIT license is pretty simple: > The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Softwa

The MIT license is pretty simple: > The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software. I would just put it in a comment at the top of turndown.js. That's enough to fulfil the license requirements. I know a lot of people don't care, but good to do it right. Definitely don't replace your license with theirs though :)