Update tutorial-document-your-models.md

[olycats]

Add customers.customer_id from the previous step

What are you changing in this pull request and why?

Quickstart for dbt Cloud and BigQuery
Step 12 Add tests to your models https://docs.getdbt.com/quickstarts/bigquery?step=12
Step 13 Document your models https://docs.getdbt.com/quickstarts/bigquery?step=13

I found that the schema.yml in step 13 is not consistent with step 12.

There is column:customer_id in step 12 but not step 13. I would like it to be added to step 13 as well.

      - name: customer_id
        tests:
          - not_null
          - relationships:
              to: ref('stg_customers')
              field: customer_id

Checklist

• Review the Content style guide and About versioning so my content adheres to these guidelines.
• Add a checklist item for anything that needs to happen before this PR is merged, such as "needs technical review" or "change base branch."

[welcome]

Hello!👋 Thanks for contributing to the dbt product documentation and opening this pull request! ✨
We use Markdown and some HTML to write the dbt product documentation. When writing content, you can use our style guide and content types to understand our writing standards and how we organize information in the dbt product docs.
We'll review your contribution and respond as soon as we can. 😄

[vercel]

@olycats is attempting to deploy a commit to the dbt-labs Team on Vercel.

A member of the Team first needs to authorize it.

[vercel]

The latest updates on your projects. Learn more about Vercel for Git ↗︎

Name	Status	Preview	Comments	Updated (UTC)
docs-getdbt-com	✅ Ready (Inspect)	Visit Preview	💬 1 unresolved	Sep 27, 2023 9:55pm

[runleonarun]

Great catch @olycats! Approving and will merge this change soon!