Adjust package documentation (#6366)

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When the Metadata team was looking into a customer issue we noticed that
their project which used a package was receiving sources from that
package. After double checking the documentation it seems that packages
only mention models and macros being part of package behavior, which is
misleading.

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🚀 Deployment available! Here are the direct links to the updated files:


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https://docs-getdbt-com-git-packagedocs-dbt-labs.vercel.app/docs/build/packages

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---------

Co-authored-by: Leona B. Campbell <[email protected]>

website/docs/docs/build/packages.md

@@ -20,9 +20,10 @@ In dbt, libraries like these are called _packages_. dbt's packages are so powerf
   * Models to understand [Redshift](https://hub.getdbt.com/dbt-labs/redshift/latest/) privileges.
   * Macros to work with data loaded by [Stitch](https://hub.getdbt.com/dbt-labs/stitch_utils/latest/).
 
-dbt _packages_ are in fact standalone dbt projects, with models and macros that tackle a specific problem area. As a dbt user, by adding a package to your project, the package's models and macros will become part of your own project. This means:
+dbt _packages_ are in fact standalone dbt projects, with models, macros, and other resources that tackle a specific problem area. As a dbt user, by adding a package to your project, all of the package's resources will become part of your own project. This means:
 * Models in the package will be materialized when you `dbt run`.
 * You can use `ref` in your own models to refer to models from the package.
+* You can use `source` to refer to sources in the package.
 * You can use macros in the package in your own project.
 * It's important to note that defining and installing dbt packages is different from [defining and installing Python packages](/docs/build/python-models#using-pypi-packages)