Document how to override vendor-data

This bug was originally filed in Launchpad as [LP: #1859720](https://bugs.launchpad.net/cloud-init/+bug/1859720)

Launchpad details

affected_projects = []

assignee = None

assignee_name = None

date_closed = None

date_created = 2020-01-14T21:41:34.922696+00:00

date_fix_committed = None

date_fix_released = None

id = 1859720

importance = medium

is_complete = False

lp_url = https://bugs.launchpad.net/cloud-init/+bug/1859720

milestone = None

owner = minagalic

owner_name = Mina Galić

private = False

status = triaged

submitter = minagalic

submitter_name = Mina Galić

tags = ['docs']

duplicates = []

_Launchpad user **Mina Galić(minagalic)** wrote on 2020-01-14T21:41:34.922696+00:00_

the vendor data documentation: https://cloudinit.readthedocs.io/en/latest/topics/vendordata.html
describes that we can override or disable vendor data, but does not explain how.

this might be causing some confusion…?
related? https://bugs.launchpad.net/cloud-init/+bug/1837530