docs(README): add mascot icon

Author: gnapse

README.md

@@ -1,6 +1,10 @@
 <div align="center">
 <h1>jest-dom</h1>
 
+<a href="https://www.emojione.com/emoji/1f989">
+<img height="80" width="80" alt="owl" src="https://raw.githubusercontent.com/gnapse/jest-dom/master/other/owl.png" />
+</a>
+
 <p>Custom jest matchers to test the dom structure</p>
 </div>