It is not that difficult as BLUI basically renders the website to a texture (it is more complicated than that but you get a basic understanding of what I mean). You would literally include this render area in your widget and than add your buttons and text areas to do what you need it to do … and you have a UMG browser.
There is no need for a tutorial … just check out the BLUI page: BLUI Open Source HTML5/JS/CSS HUD/UI