Select resources with the source resource_type (#4145)

[Preview](https://docs-getdbt-com-git-dbeatty-source-resource-type-dbt-labs.vercel.app/reference/node-selection/methods#the-resource_type-method)

## What are you changing in this pull request and why?

dbt-labs/dbt-core#8730 surfaced an area to
provide more precise guidance how to select sources.


## 🎩 

Before:

<img width="832" alt="image"
src="https://github.com/dbt-labs/docs.getdbt.com/assets/44704949/5b97eb54-3669-417c-8332-581609d2fec1">

After:

<img width="839" alt="image"
src="https://github.com/dbt-labs/docs.getdbt.com/assets/44704949/056abc36-96f1-441e-8667-3208d074cc1d">


## Checklist
- [x] Review the [Content style
guide](https://github.com/dbt-labs/docs.getdbt.com/blob/current/contributing/content-style-guide.md)
and [About
versioning](https://github.com/dbt-labs/docs.getdbt.com/blob/current/contributing/single-sourcing-content.md#adding-a-new-version)
so my content adheres to these guidelines.

website/docs/reference/node-selection/methods.md

@@ -47,13 +47,19 @@ The `source` method is used to select models that select from a specified [sourc
   ```
 
 ### The "resource_type" method
-Use the `resource_type` method to select nodes of a particular type (`model`, `source`, `exposure`, etc). This is similar to the `--resource-type` flag used by the [`dbt ls` command](/reference/commands/list).
+Use the `resource_type` method to select nodes of a particular type (`model`, `test`, `exposure`, and so on). This is similar to the `--resource-type` flag used by the [`dbt ls` command](/reference/commands/list).
 
   ```bash
   $ dbt build --select resource_type:exposure    # build all resources upstream of exposures
   $ dbt list --select resource_type:test    # list all tests in your project
   ```
 
+Note: This method doesn't work for sources, so use the [`--resource-type`](/reference/commands/list) option of the list command instead:
+
+  ```bash
+  $ dbt list --resource-type source
+  ```
+
 ### The "path" method
 The `path` method is used to select models/sources defined at or under a specific path.
 Model definitions are in SQL/Python files (not YAML), and source definitions are in YAML files.