Docker installation method

[alangecker]

as requested by @matiasilva this PR adds the docker installation method to the documentation.

closes alangecker/bigbluebutton-docker#15

[basisbit]

There are still these "Open tasks" mentioned in the readme of that repository:

• add support for recording
• add prometheus exporter
• further separate bbb-core into individual container
• enable IPv6 support
• switch html5 to node v12
• drop root privileges in webrtc-sfu

I'd suggest to not merge this until a certain quality and completeness has been reached.

[alangecker]

There are still these "Open tasks" mentioned in the readme of that repository:
[...]

I'd suggest to not merge this until a certain quality and completeness has been reached.

these points are just nice to have and neither included in the other installation methods so I don't think that they are somehow relevant as a blocking issue.

• add prometheus exporter
• switch html5 to node v12 (other methods rely on node v8)
• further separate bbb-core into individual container (other methods don't work with isolation of components)

but yeps, these two can be considered as blocking issues:

• missing recording
• missing IPv6 support

[alangecker]

so, both blocking issues are resolved with the latest Release v2.2.23-1
@basisbit I would be happy about continuing the discussion, especially what further requirement / concerns you see for adding this method :)

[ffdixon]

@alangecker We can merge this in for 2.4 if you can resolve the merge conflicts.