Docs for setting up a BQ client

[ianlewis]

It seems that criticality_score tries to detect a project ID to execute BigQuery queries. It would be nice to have a bit of documentation that this is needed, and how to set it up.

2023-06-14 06:29:39.253 ERROR   Failed to create collector      {"error": "init deps.dev source: failed to create bigquery client: unable to detect projectID, please refer to docs for DetectProjectID"}                                                                                                                                                                  
main.main                                                                      
        /usr/local/google/home/ianlewis/go/pkg/mod/github.com/ossf/criticality_score@v1.0.8/cmd/criticality_score/main.go:160
runtime.main
        /usr/local/google/home/ianlewis/opt/go/src/runtime/proc.go:250