st2chatops dockerfile readme incomplete

[MrDiba]

As it is required to enable st2chatops by setting the environment variable ST2_CHATOPS_ENABLE before using the container, this should be added to the readme as a required variable.

[arm4b]

Thanks for the report!

I think it's documented here already: https://github.com/stackStorm/st2-docker#compose-configuration

Just setting the ENV variable in this repository won't have effect as the configuration is relevant to docker-compose repository above and not container specific.

Hope that helps.

[MrDiba]

Ah okay, I understand! Thank you for the explanation.