[BUG] Alerts can be deleted in the case history (#4756)

* Updating note

* Minor edit

* Update docs/detections/alerts-add-to-cases.asciidoc

(cherry picked from commit cdf7f90)

docs/detections/alerts-add-to-cases.asciidoc

@@ -7,7 +7,7 @@
 
 From the Alerts table, you can attach one or more alerts to a <<signals-to-new-cases,new case>> or <<signals-to-existing-cases,an existing one>>. Alerts from any rule type can be added to a case.
 
-NOTE: Once you've added an alert to a case, you can only remove it through the <<cases-api-overview,Elastic Security Cases API>>.
+NOTE: After you add an alert to a case, you can remove it from the case activity under the alert summary or by using the <<cases-api-overview,Elastic Security Cases API>>.
 
 [role="screenshot"]
 image::images/add-alert-to-case.gif[width=50%][height=50%][Animation of adding an alert to a case]