Update Readme and add description for the fork.

Author: leonzz

README.md

@@ -1,5 +1,7 @@
 # go-diskqueue
 
+This is a fork of https://github.com/nsqio/go-diskqueue with the additional support of total disk space limit.
+
 [![Build Status](https://travis-ci.com/kev1n80/go-diskqueue.svg?branch=master)](https://travis-ci.com/github/kev1n80/go-diskqueue) [![Go Reference](https://pkg.go.dev/badge/github.com/kev1n80/go-diskqueue.svg)](https://pkg.go.dev/github.com/kev1n80/go-diskqueue) [![GitHub release](https://img.shields.io/github/release/kev1n80/go-diskqueue.svg)](https://github.com/kev1n80/go-diskqueue/releases/latest)
 
 A Go package providing a filesystem-backed FIFO queue