Create Plone 6.3 upgrade guide placeholder (#2085)

* Create Plone 6.3 upgrade guide placeholder

* - Add to 6.3 to toctree at upgrade/index

---------

Co-authored-by: Maurits van Rees <maurits@vanrees.org>

Author: stevepiercy

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

@@ -28,5 +28,6 @@ upgrade-zodb-to-python3
 upgrade-to-60
 upgrade-to-61
 upgrade-to-62
+upgrade-to-63
 migrate-to-volto
 ```

docs/backend/upgrading/version-specific-migration/upgrade-to-63.md

@@ -0,0 +1,16 @@
+---
+myst:
+  html_meta:
+    "description": "How to upgrade to Plone 6.3"
+    "property=og:description": "How to upgrade to Plone 6.3"
+    "property=og:title": "How to upgrade to Plone 6.3"
+    "keywords": "Upgrade, Plone 6"
+---
+
+(backend-upgrade-plone-v63-label)=
+
+# Upgrade Plone 6.2 to 6.3
+
+Plone 6.3 has seen the following major changes.
+Some may require changes in your setup.
+

docs/upgrade/index.md

@@ -19,6 +19,7 @@ Plone has several components, each of which have their own upgrade guides:
 
 For Plone 6 the most relevant guides are:
 
+-   {doc}`../backend/upgrading/version-specific-migration/upgrade-to-63`
 -   {doc}`../backend/upgrading/version-specific-migration/upgrade-to-62`
 -   {doc}`../backend/upgrading/version-specific-migration/upgrade-to-61`
 -   {doc}`../backend/upgrading/version-specific-migration/upgrade-to-60`