readme: Update agave logo (#6597)

README.md

@@ -1,6 +1,6 @@
 <p align="center">
   <a href="https://anza.xyz">
-    <img alt="Anza" src="https://i.imgur.com/0vfIMHo.png" width="250" />
+    <img alt="Anza" src="https://i.postimg.cc/VkKTnMM9/agave-logo-talc-1.png" width="250" />
   </a>
 </p>