Add documentation for the severed_relationships event type (#1385)

* Add documentation for the `severed_relationships` event type
* Create RelationshipSeveranceEvent.md

content/en/entities/Notification.md

@@ -35,13 +35,15 @@ aliases: [
 `update` = A status you interacted with has been edited\
 `admin.sign_up` = Someone signed up (optionally sent to admins)\
 `admin.report` = A new report has been filed\
+`severed_relationships` = Some of your follow relationships have been severed as a result of a moderation or block event\
 **Version history:**\
 0.9.9 - added\
 2.8.0 - added `poll`\
 3.1.0 - added `follow_request`\
 3.3.0 - added `status`\
 3.5.0 - added `update` and `admin.sign_up`\
-4.0.0 - added `admin.report`
+4.0.0 - added `admin.report`\
+4.3.0 - added `severed_relationships`
 
 ### `created_at` {#created_at}
 
@@ -71,6 +73,13 @@ aliases: [
 **Version history:**\
 4.0.0 - added
 
+### `relationship_severance_event` {{%optional%}} {#relationship_severance_event}
+
+**Description:** Summary of the event that caused follow relationships to be severed. Attached when `type` of the notification is `severed_relationships`.\
+**Type:** [RelationshipSeveranceEvent]({{< relref "entities/RelationshipSeveranceEvent" >}})\
+**Version history:**\
+4.3.0 - added
+
 ## Examples
 
 ### Mention

content/en/entities/RelationshipSeveranceEvent.md

@@ -0,0 +1,58 @@
+---
+title: RelationshipSeveranceEvent
+description: Summary of a moderation or block event that caused follow relationships to be severed.
+menu:
+  docs:
+    parent: entities
+aliases: [
+  "/entities/RelationshipSeveranceEvent",
+  "/api/entities/RelationshipSeveranceEvent",
+]
+---
+
+## Attributes
+
+### `id` {#id}
+
+**Description:** The ID of the relationship severance event in the database.\
+**Type:** String (cast from integer)\
+**Version history:**\
+4.3.0 - added
+
+### `type` {#type}
+
+**Description:** Type of event.\
+**Type:** String (Enumerable oneOf)\
+`domain_block` = A moderator suspended a whole domain\
+`user_domain_block` = The user blocked a whole domain\
+`account_suspension` = A moderator suspended a specific account\
+**Version history:**\
+4.3.0 - added
+
+### `purged` {#purged}
+
+**Description:** Whether the list of severed relationships is unavailable because the underlying issue has been purged.\
+**Type:** Boolean\
+**Version history:**\
+4.3.0 - added
+
+### `target_name` {#target_name}
+
+**Description:** Name of the target of the moderation/block event. This is either a domain name or a user handle, depending on the event type.\
+**Type:** String\
+**Version history:**\
+4.3.0 - added
+
+### `relationships_count` {{%optional%}} {#relationships_count}
+
+**Description:** Number of follow relationships (in either direction) that were severed.\
+**Type:** Integer\
+**Version history:**\
+4.3.0 - added
+
+### `created_at` {#created_at}
+
+**Description:** When the event took place.\
+**Type:** String (ISO 8601 Datetime)\
+**Version history:**\
+4.3.0 - added