Update README.md

Remove the word simple. It does a lot of complex things.

README.md

@@ -2,7 +2,7 @@
 
 ![Badger mascot](images/diggy-shadow.png)
 
-BadgerDB is an embeddable, persistent, simple and fast key-value (KV) database
+BadgerDB is an embeddable, persistent and fast key-value (KV) database
 written in pure Go. It's meant to be a performant alternative to non-Go-based
 key-value stores like [RocksDB](https://github.com/facebook/rocksdb).