Start Plone 6.1 upgrade guide

Author: stevepiercy

docs/backend/upgrading/version-specific-migration/index.md

@@ -26,5 +26,6 @@ upgrade-to-52
 upgrade-to-python3
 upgrade-zodb-to-python3
 upgrade-to-60
+upgrade-to-61
 migrate-to-volto
 ```

docs/backend/upgrading/version-specific-migration/upgrade-to-61.md

@@ -0,0 +1,27 @@
+---
+myst:
+  html_meta:
+    "description": "How to upgrade to Plone 6.1"
+    "property=og:description": "How to upgrade to Plone 6.1"
+    "property=og:title": "How to upgrade to Plone 6.1"
+    "keywords": "Upgrade, Plone 6"
+---
+
+(backend-upgrade-plone-v61-label)=
+
+# Upgrade Plone 6.0 to 6.1
+
+Plone 6.1 has seen the following major changes.
+Some may require changes in your setup.
+
+
+## TinyMCE upgraded
+
+Plone 6.0 uses TinyMCE, a rich text editor for websites.
+TinyMCE 5 reached its end of support on April 20, 2023.
+For Plone 6.1, TinyMCE has been upgraded from version 5 to 7.
+
+```{seealse}
+-   [How to upgrade TinyMCE 5 to TinyMCE 6](https://www.tiny.cloud/blog/upgrade-to-tinymce-6/)
+-   [Upgrading TinyMCE](https://www.tiny.cloud/docs/tinymce/latest/upgrading/)
+```