Issue in explaining the usage of broker-api

[JimmyMalark]

Describe the bug
There is a bug in explaining usage of broker-api in command line

To Reproduce
Steps to reproduce the behavior:

1. Go to https://flower.readthedocs.io/en/latest/config.html#id36
2. Click on broker-api
3. See broker api usage in command line after celery flower ...

Expected behavior
It should say celery flower --broker-api=... not broker-api=...

Screenshots