add polygon rounding examples

Author: astearns

css-shapes-1/Overview.bs

@@ -498,6 +498,15 @@ Supported Shapes</h3>
 				and that is tangential 
 				to both sides of the vertex.
 
+				<div class="example">
+					<figure>
+						<img src="images/vertex-rounding.png" alt="rounding concave and convex polygon vertices">
+						<figcaption>
+							Rounding polygon vertices that are both convex and concave.
+						</figcaption>
+					</figure>
+				</div>
+
 				To avoid rounding more
 				than half of any line segment,
 				the rounding of each vertex 
@@ -506,8 +515,14 @@ Supported Shapes</h3>
 				the smaller of <code>tan(angle/2) segment / 2</code> 
 				evaluated against both vertex line segments.
 
-
-			Note: vertex rounding needs examples and tests.
+				<div class="example">
+					<figure>
+						<img src="images/clamp-explanation.png" alt="visualization of clamp formula">
+						<figcaption>
+							This diagram shows the intent of the clamping formula.
+						</figcaption>
+					</figure>
+				</div>
 
 			* Each <<length-percentage>> pair
 				specifies a vertex of the polygon,