Update Migration guide after major release

Author: dvacca-onfido

.markdownlint.json

@@ -0,0 +1,3 @@
+{
+  "MD024": false
+}

MIGRATION.md

@@ -1,5 +1,34 @@
 # Migration Guide
 
+This guide provides detailed instructions on how to upgrade between different
+major versions of the client library.
+
+It covers changes in core resources, other endpoints, and the OpenAPI generator,
+ensuring a smooth transition between versions.
+
+## Upgrading from 4.x to 5.x
+
+### Core Resources
+
+- Documents
+  - Allow any string as `file_type`
+
+### Other Endpoints
+
+- Webhooks
+  - Drop `WORKFLOW_SIGNED_EVIDENCE_FILE_DOT_CREATED` enum value from
+    `WebhookEventType` enum
+  - Make `href` property in `WebhookEventPayloadObject` optional
+- Reports
+  - Allow the deprecated `records` property in `WatchlistAml` and
+    `WatchlistStandard` reports to be any object, and not just a string
+  - Remove `documents` property from all reports except Document and
+    Facial Similarity reports
+
+### OpenAPI generator
+
+- Version upgraded from `7.9.0` to `7.11.0`
+
 ## Upgrading from 3.x to 4.x
 
 ### Core Resources
@@ -27,5 +56,5 @@
 
 ### OpenAPI generator
 
-- Version upgraded from 7.6.0 to 7.9.0
+- Version upgraded from `7.6.0` to `7.9.0`
   - Remove support for python 3.7