[ci skip] improve readme

Author: dustin deus

README.md

@@ -4,7 +4,7 @@
 
 Optimized JSON HTTP Data Source for Apollo Server
 
-- Uses [Undici](https://github.com/nodejs/undici) under the hood
+- Uses [Undici](https://github.com/nodejs/undici) under the hood. It's around `54%` faster than `apollo-datasource-rest`
 - Request Deduplication (LRU), Request Cache (TTL) and `stale-if-error` Cache (TTL)
 - Support [AbortController ](https://github.com/mysticatea/abort-controller) to manually cancel all running requests
 - Support for [Apollo Cache Storage backend](https://www.apollographql.com/docs/apollo-server/data/data-sources/#using-memcachedredis-as-a-cache-storage-backend)