[improvement] No documentation of the effects of connecting Plugs

[KlfJoat]

There are a few Plugs not connected to Slots by default when the Discord snap is installed.

Specifically they are:

1. discord:mount-observe
2. discord:network-observe
3. discord:process-control
4. discord:removable-media
5. discord:system-observe

I cannot find anywhere that explains what each plug will allow Discord to do when connected to its slot.

Some of them seem obvious, but not being an expert I might misunderstand them. Others, like discord:system-observe, are recommended by the snapcrafters to connect with only a vague mention of the primary effect(s) ("enable the features") and a reasonably concrete mention of a secondary effect ("reduce the logging"). I think the primary effect(s) should be documented for me to make an informed decision of whether the log spam is better than enabling the plug.

Is Discord's inability to tell that I'm inactive, and thus push notifications to my mobile device, a function of one of those plugs not being connected? I sure don't know. But documentation might help me to find out.