[DOCS] Adds empty snapshot_id description to revert snapshot API docs (#66036)

docs/reference/ml/anomaly-detection/apis/get-snapshot.asciidoc

@@ -15,6 +15,7 @@ Retrieves information about model snapshots.
 
 `GET _ml/anomaly_detectors/<job_id>/model_snapshots/<snapshot_id>`
 
+
 [[ml-get-snapshot-prereqs]]
 == {api-prereq-title}
 
@@ -22,6 +23,7 @@ Retrieves information about model snapshots.
 `monitor`, `manage_ml`, or `manage` cluster privileges to use this API. See
 <<security-privileges>> and {ml-docs-setup-privileges}.
 
+
 [[ml-get-snapshot-path-parms]]
 == {api-path-parms-title}
 
@@ -40,6 +42,7 @@ You can get all snapshots for all calendars by using `_all`,
 by specifying `*` as the `<snapshot_id>`, or by omitting the `<snapshot_id>`.
 --
 
+
 [[ml-get-snapshot-request-body]]
 == {api-request-body-title}
 

docs/reference/ml/anomaly-detection/apis/revert-snapshot.asciidoc

@@ -42,6 +42,12 @@ include::{es-repo-dir}/ml/ml-shared.asciidoc[tag=job-id-anomaly-detection]
 `<snapshot_id>`::
 (Required, string)
 include::{es-repo-dir}/ml/ml-shared.asciidoc[tag=snapshot-id]
++
+--
+You can specify `empty` as the <snapshot_id>. Reverting to the `empty` snapshot 
+means the {anomaly-job} starts learning a new model from scratch when it is 
+started.
+--
 
 [[ml-revert-snapshot-request-body]]
 == {api-request-body-title}