Update the sidebar

[jajik]

There are links to only Java's part GitHub, it would be nice to add native part too.

Additionally, there is a link to a docker image that was last updated five years ago. We should remove the link or create a new image and link to that – do we want it? If so, I suggest creating appropriate folder within the source repo.

[rhusar]

Right...

This page links to all sources - https://www.modcluster.io/source-code/
Github links to org - https://github.com/modcluster

So the downloads + docker links should be improved

[rhusar]

Dockerhub "fix" - #43

There are no native downloads link to fix with (yet)