docs: Kirby VTT banner

Author: pdbethke

README.md

@@ -1,3 +1,7 @@
+<p align="center">
+  <img src="docs/kirby-vtt.jpg" alt="Kirby VTT — a comic panel in the Kirby style: a caped, armoured figure lettered KV bursting forward through exploding stars and crackling energy." width="900">
+</p>
+
 # kirby-cost
 
 [![PyPI](https://img.shields.io/pypi/v/kirby-cost)](https://pypi.org/project/kirby-cost/)