dvc.yaml: mention that there can be more than one per project

per #1641

content/docs/command-reference/repro.md

@@ -24,11 +24,11 @@ positional arguments:
 
 `dvc repro` provides a way to regenerate data pipeline results, by restoring the
 dependency graph (a [DAG](https://en.wikipedia.org/wiki/Directed_acyclic_graph))
-implicitly defined by the stages listed in `dvc.yaml`. The commands defined in
-these stages are then executed in the correct order, reproducing pipeline
-results.
+implicitly defined by the stages listed in `dvc.yaml` files. The commands
+defined in these stages are then executed in the correct order, reproducing
+pipeline results.
 
-> Pipeline stages are defined in a `dvc.yaml` file (either manually or by using
+> Pipeline stages are defined in `dvc.yaml` (either manually or by using
 > `dvc run`) while initial data dependencies can be registered with `dvc add`.
 
 This command is similar to [Make](https://www.gnu.org/software/make/) in

content/docs/command-reference/root.md

@@ -27,11 +27,14 @@ Use this command to build fixed paths to dependencies, files, or stage
 
 - `-v`, `--verbose` - displays detailed tracing information.
 
-## Example: Basic output
+## Examples
+
+Basic demonstration:
 
 ```dvc
 $ dvc root
 .
+
 $ mkdir subdir
 $ cd subdir
 $ dvc root

content/docs/user-guide/dvc-files-and-directories.md

@@ -187,7 +187,11 @@ the following fields:
 
 `dvc.yaml` files also support `# comments`.
 
-💡 We maintain a `dvc.yaml`
+💡 Keep in mind that there may be more than one `dvc.yaml` files in each
+<abbr>DVC project</abbr>. DVC checks all of them for consistency during
+operations that require rebuilding DAGs (like `dvc dag`).
+
+Note that we maintain a `dvc.yaml`
 [schema](https://github.com/iterative/dvcyaml-schema) that can be used by
 editors like [VSCode](/doc/install/plugins#visual-studio-code) or
 [PyCharm](/doc/install/plugins#pycharmintellij) to enable automatic syntax