Link out to placeholder upgrade guide from changelog

Author: consideRatio

docs/source/administrator/upgrading/index.md

@@ -22,6 +22,7 @@ or the [Discourse forum](https://discourse.jupyter.org/).
 :maxdepth: 1
 :caption: Major releases guides
 
+upgrade-3-to-4
 upgrade-2-to-3
 upgrade-1-to-2
 ```

docs/source/administrator/upgrading/upgrade-1-to-2.md

@@ -1,3 +1,5 @@
+(upgrade-1-to-2)=
+
 # Major upgrade: 1.\* to 2.\*
 
 Z2JH 2 contains several breaking changes, including some that affect the security of your deployment.

docs/source/administrator/upgrading/upgrade-2-to-3.md

@@ -1,3 +1,5 @@
+(upgrade-2-to-3)=
+
 # Major upgrade: 2.\* to 3.\*
 
 Z2JH 3 contains some small breaking changes.

docs/source/administrator/upgrading/upgrade-3-to-4.md

@@ -0,0 +1,5 @@
+(upgrade-3-to-4)=
+
+# Major upgrade: 3.\* to 4.\*
+
+This is currently just a placeholder file for until we have written upgrade docs.

docs/source/changelog.md

@@ -16,9 +16,11 @@ changes in pull requests], this list should be updated.
 
 ### 4.0.0-beta.1 - 2024-10-XX
 
-TODO: provide summarizing paragraph here
-TODO: link to upgrade notes
-TODO: include notable dependency changes like in previous major release
+TODO: write a release summary here.
+
+This changelog is just providing an overview of changes, so its meant to be
+complemented with the [major version upgrade documentation](upgrade-3-to-4) with
+practical advice on upgrading accounting for changes.
 
 #### Breaking changes