add codefactor badge

README.md

@@ -17,6 +17,7 @@
 [![CII Best Practices](https://bestpractices.coreinfrastructure.org/projects/3563/badge)](https://bestpractices.coreinfrastructure.org/projects/3563)
 [![codecov](https://codecov.io/gh/milvus-io/milvus/branch/master/graph/badge.svg)](https://codecov.io/gh/milvus-io/milvus)
 [![codebeat badge](https://codebeat.co/badges/e030a4f6-b126-4475-a938-4723d54ec3a7?style=plastic)](https://codebeat.co/projects/github-com-milvus-io-milvus-master)
+[![CodeFactor Grade](https://www.codefactor.io/repository/github/milvus-io/milvus/badge)](https://www.codefactor.io/repository/github/milvus-io/milvus)
 [![Codacy Badge](https://api.codacy.com/project/badge/Grade/c4bb2ccfb51b47f99e43bfd1705edd95)](https://app.codacy.com/gh/milvus-io/milvus?utm_source=github.com&utm_medium=referral&utm_content=milvus-io/milvus&utm_campaign=Badge_Grade_Dashboard)
 [![Scrutinizer Quality Score](https://scrutinizer-ci.com/g/milvus-io/milvus/badges/quality-score.png?b=master)](https://scrutinizer-ci.com/g/milvus-io/milvus/)