[css-inline] illustration of float interaction per dbaron example from Seattle F2F

Author: dauwhe

css-inline-3/Overview.bs

@@ -1271,6 +1271,16 @@ Interaction with floats</h4>
 			in subsequent lines of content adjacent to a (sunk) <a>initial letter</a>,
 			then that float must clear the <a>initial letter</a>.
 	</ul>
+	
+		<figure>
+		<img src="images/float-interaction.png" width="480"
+		     alt="initial letter interacting with floats">
+		<figcaption>
+			In the absence of an initial letter, the first line of text could abut the blue float. 
+			But the presence of the initial letter requires that the text move over.
+		</figcaption>
+	</figure>
+
 
 	See <a href="https://www.w3.org/TR/CSS21/visuren.html#floats">CSS2&sect;9.5</a>
 	for more information about the layout of floats