client: document package
client: document package

Change-Id: Id753622aded1f846a8445a6946c8374bb6eae06a
Reviewed-on: https://team-review.git.corp.google.com/c/golang/vulndb/+/1063695
Reviewed-by: Roland Shoemaker <2291a4863372ad77fa6806f7776fa8f1d387bc05@google.com>

golang/vuln,golang/vuln