Update badges in README.md (#1654)

Author: gkorland

README.md

@@ -2,10 +2,11 @@
 
 The Python interface to the Redis key-value store.
 
-[![image](https://github.com/redis/redis-py/workflows/CI/badge.svg?branch=master)](https://github.com/redis/redis-py/actions?query=workflow%3ACI+branch%3Amaster) 
-[![image](https://readthedocs.org/projects/redis-py/badge/?version=stable&style=flat)](https://redis-py.readthedocs.io/en/stable/) 
-[![image](https://badge.fury.io/py/redis.svg)](https://pypi.org/project/redis/) 
+[![CI](https://github.com/redis/redis-py/workflows/CI/badge.svg?branch=master)](https://github.com/redis/redis-py/actions?query=workflow%3ACI+branch%3Amaster) 
+[![docs](https://readthedocs.org/projects/redis-py/badge/?version=stable&style=flat)](https://redis-py.readthedocs.io/en/stable/) 
+[![pypi](https://badge.fury.io/py/redis.svg)](https://pypi.org/project/redis/) 
 [![codecov](https://codecov.io/gh/redis/redis-py/branch/master/graph/badge.svg?token=yenl5fzxxr)](https://codecov.io/gh/redis/redis-py)
+[![Total alerts](https://img.shields.io/lgtm/alerts/g/redis/redis-py.svg?logo=lgtm&logoWidth=18)](https://lgtm.com/projects/g/redis/redis-py/alerts/)
 
 
 ## Python 2 Compatibility Note