Update readme with new util decode method

Author: ianopolous

README.md

@@ -16,7 +16,8 @@ Simply clone this repository.
 ## Usage
 
 ```
-Multihash m = Multihash.fromBase58("QmatmE9msSfkKxoffpHwNLNKgwZG8eT9Bud6YoPab52vpy");
+Multihash b58 = Multihash.decode("QmatmE9msSfkKxoffpHwNLNKgwZG8eT9Bud6YoPab52vpy");
+Multihash b36 = Multihash.decode("kmue2y4illvr0m3lt8x6z8iwghtxlzdmkjh957p5rr5cdr9243ugc");
 ```
 ## Dependency
 You can use this project by building the JAR file as specified below, or by using [JitPack](https://jitpack.io/#multiformats/java-multihash/) (also supporting Gradle, SBT, etc).