document the static mirror network and onionbalance system better

we have some documentation on the static mirroring system here:

https://help.torproject.org/tsa/howto/static-component/

it's mostly procedural and minimal: add a component, remove a component and that's it. it doesn't explain at all how the system works, how to create or remove a new node in the network, how onion services interact with it, and how it actually works in puppet.

all this should be better documented. for example, I should be able to resolve legacy/trac#34396 (moved) without asking weasel. :)