Document how to install plugins on multisite environment

[aerugo]

As we scale the org, we will need to make sure that more people can carry out routine updates. This requires some documentation of the multisite environment. One thing that needs to be documented is how to add and update plugins.

[tanius]

I am taking this over from @damingo. There are some notes I got and I'll basically have to make a manual and follow the whole process once from the beginning of the installation.

Could take a bit due to time constraints. In the meantime, please tell @damingo to do any updates or deployments of plugins if needed.

Once multiple people start to make live version changes, we will also need a changelog so somebody else can debug in case something breaks …