Update documentation about usage of local tokeninfo

[lmineiro]

Usage of the local tokeninfo sidecar is not properly documented. The flag

local_planb_tokeninfo: true

Can be used to enable the local sidecar but this doesn't seem to be visible in the documentation.

I believe it also requires

networking: host

to work properly. Should be checked and clear in the docs

[AlexanderYastrebov]

Related to https://github.com/zalando-stups/taupage/issues/307