Looks great in Sigil - you'll have to create the float-left (or float-whatever) property in CSS:
img.float-left{
float:left;
}
And then you can use margins around your images to make it look better.
Possible also to do with text, like if you have a call-out box. Pretty cool!
You'll need to add the class to the img tag:
<img class="float-left" />