doc: refer to audit section in the upspin docs
doc: refer to audit section in the upspin docs

This is where the docs actually are. The command docs are a stub.

Change-Id: Idcfd5f5a60da5c5de4b5a040132289f2fa0a8251
Reviewed-on: https://upspin-review.googlesource.com/17700
Reviewed-by: Rob Pike <4dc7c9ec434ed06502767136789763ec11d2c4b7@golang.org>

upspin/upspin,upspin/upspin