add logo to top of readme

I picked Raleway because it's flow-y and has some serif-y elements
that call out to the tradition of typography which CSS is always
drawing from. Text flowing into available space is like a natural
process, so I used a raindrop to connote nature. I originally used
"drop" because block boxes drop down, but I like the feeling of
nature better.

README.md

@@ -1,4 +1,4 @@
-# dropflow
+<img height=50 src=assets/logo.png>
 
 Dropflow is a CSS layout engine created to explore the reaches of the foundational CSS standards (that is: inlines, blocks, floats, positioning and eventually tables, but not flexbox or grid). It has a high quality text layout implementation and is capable of displaying many of the languages of the world. You can use it to generate PDFs or images on the backend with Node and [node-canvas](https://github.com/Automattic/node-canvas) or render rich, wrapped text to a canvas in the browser.