Artifacts: When to use save() vs .log() (#1557)

Description
-----------
Adds quick blurb on "best practice"/recommendation by Eng on when to use
which.


Related issues
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- Fixes
https://wandb.atlassian.net/jira/software/projects/DOCS/boards/28?selectedIssue=DOCS-1087

Author: ngrayluna

content/en/guides/core/artifacts/construct-an-artifact.md

@@ -69,7 +69,10 @@ run = wandb.init(project="artifacts-example", job_type="job-type")
 run.log_artifact(artifact)
 ```
 
-You can optionally construct an artifact outside of a W&B run. For more information, see [Track external files]({{< relref "./track-external-files.md" >}}).
+{{% alert title="When to use Artifact.save() or wandb.Run.log_artifact()"  %}}
+- Use `Artifact.save()` to update an existing artifact without creating a new run.
+- Use `wandb.Run.log_artifact()` to create a new artifact and associate it with a specific run.
+{{% /alert %}}
 
 {{% alert color="secondary" %}}
 Calls to `log_artifact` are performed asynchronously for performant uploads. This can cause surprising behavior when logging artifacts in a loop. For example:

content/en/guides/core/artifacts/update-an-artifact.md

@@ -10,6 +10,11 @@ weight: 4
 
 Pass desired values to update the `description`, `metadata`, and `alias` of an artifact. Call the `save()` method to update the artifact on the W&B servers. You can update an artifact during a W&B Run or outside of a Run.
 
+{{% alert title="When to use Artifact.save() or wandb.Run.log_artifact()"  %}}
+- Use `Artifact.save()` to update an existing artifact without creating a new run.
+- Use `wandb.Run.log_artifact()` to create a new artifact and associate it with a specific run.
+{{% /alert %}}
+
 Use the W&B Public API ([`wandb.Api`]({{< relref "/ref/python/public-api/api.md" >}})) to update an artifact outside of a run. Use the Artifact API ([`wandb.Artifact`]({{< relref "/ref/python/sdk/classes/artifact.md" >}})) to update an artifact during a run.
 
 {{% alert color="secondary" %}}