doc: suggest Setting up upspinserver doc instead of Google Cloud one
doc: suggest Setting up upspinserver doc instead of Google Cloud one

The recommended way to run your own cluster is to deploy upspinserver to
a stand-alone server, rather than somewhat deprecated the Deploying
Upspin to Google Cloud.

Change-Id: Iaecad0e6628eea1328dabd1ad4c125382108d012
Reviewed-on: https://upspin-review.googlesource.com/7910
Reviewed-by: David Presotto <516b9783fca517eecbd1d064da2d165310b19759@google.com>

upspin/upspin,upspin/upspin