add an explanation of the dns weight algorithm to the docs

[gruns]

right now, its hard and opaque for node operators to understand how their node's dns weight is calculated. and dns weight is directly correlated with earnings

this can be a bit frustrating for node ops who don't understand why their weight is lower than expected, and thus earnings may be lower than expected, too

an explanation of how dns weights are calculated would be super helpful! 🙌

in the docs, including actions for the node op to take, like things to check or actions to take on their server to improve their dns weight, should be included wherever possible

cc @Reiers