docs: Add Margelo Banner (https://margelo.io)

Author: mrousavy

README.md

@@ -1,3 +1,7 @@
+<a href="https://margelo.io">
+  <img src="./img/banner.svg" width="100%" />
+</a>
+
 <div align="center">
   <h1 align="center">MMKV</h1>
   <h3 align="center">The fastest key/value storage for React Native.</h3>