Enhance README with SDK functionality description

Added a brief description of the REST API SDK's functionality.

Author: roncohen

packages/rest-api-sdk/README.md

@@ -1,11 +1,12 @@
 # @reflag/rest-api-sdk (beta)
 
 Typed SDK for Reflag's REST API.
+The REST API SDK is a management API which lets you list flags and toggle flags for users and companies amongst other things.
 
 ## Installation
 
 ```bash
-npm install @reflag/rest-api-sdk
+npm i @reflag/rest-api-sdk
 # or
 yarn add @reflag/rest-api-sdk
 ```