metrics: info on non-output usage (#3387)

* metrics: info on non-output usage

Fixes: #1909

* Update content/docs/command-reference/metrics/index.md

* Update content/docs/command-reference/metrics/show.md

Co-authored-by: Paweł Redzyński <[email protected]>

* Restyled by prettier (#3412)

Co-authored-by: Restyled.io <[email protected]>

Co-authored-by: Jorge Orpinel <[email protected]>
Co-authored-by: restyled-io[bot] <32688539+restyled-io[bot]@users.noreply.github.com>
Co-authored-by: Restyled.io <[email protected]>

Author: 4 people

content/docs/command-reference/metrics/index.md

@@ -47,8 +47,9 @@ Path          Metric    HEAD      workspace  Change
 metrics.json  AUC       0.763981  0.801807   0.037826
 ```
 
-`dvc metrics` subcommands by default use the metrics files specified in
-`dvc.yaml` (if any), for example `summary.json` below:
+`dvc metrics` subcommands can be used on any
+[valid metrics files](#supported-file-formats). By default they use the ones
+specified in `dvc.yaml` (if any), for example `summary.json` below:
 
 ```yaml
 stages:

content/docs/command-reference/metrics/show.md

@@ -27,8 +27,8 @@ target can even be directories, so that DVC recursively shows all metrics files
 inside.
 
 > Note that targets don't necessarily have to be defined in `dvc.yaml`. For that
-> reason, this command doesn't require an existing DVC project to run in; It
-> works in any Git repo.
+> reason, this command doesn't require an existing DVC project or Git repo to
+> run in.
 
 An alternative way to display metrics is the `dvc metrics diff` command, which
 compares them with a previous version.