Update the status badge to pegasus-kv/rocksdb's own (#18)

apache/incubator-pegasus#1575

1. Update the status badge to pegasus-kv/rocksdb's own site.
2. Also aim to check whether all tests could pass after cherry-picking
encryption related
patches to 8.5.3 branch.

README.md

@@ -1,6 +1,6 @@
 ## RocksDB: A Persistent Key-Value Store for Flash and RAM Storage
 
-[![CircleCI Status](https://circleci.com/gh/facebook/rocksdb.svg?style=svg)](https://circleci.com/gh/facebook/rocksdb)
+[![nightly](https://github.com/pegasus-kv/rocksdb/actions/workflows/nightly.yml/badge.svg)](https://github.com/pegasus-kv/rocksdb/actions/workflows/nightly.yml)
 
 RocksDB is developed and maintained by Facebook Database Engineering Team.
 It is built on earlier work on [LevelDB](https://github.com/google/leveldb) by Sanjay Ghemawat ([email protected])