Add badge in head: Number of Categories

README.md

@@ -14,6 +14,9 @@
     <a href="https://github.com/public-apis/public-apis/actions?query=workflow%3A%22Validate+links%22">
         <img alt="Validate links" src="https://github.com/public-apis/public-apis/workflows/Validate%20links/badge.svg?branch=master" />
     </a>
+    <a href="https://github.com/public-apis/public-apis">
+        <img alt="Number of Categories" src="https://img.shields.io/badge/dynamic/json?url=https://api.publicapis.org/categories&label=Number%20of%20Categories&query=$.count&color=informational" />
+    </a>
     <a href="https://github.com/public-apis/public-apis">
         <img alt="Number of APIs" src="https://img.shields.io/badge/dynamic/json?url=https://api.publicapis.org/entries&label=Number%20of%20APIs&query=$.count&color=informational" />
     </a>