Add a section about upgrading to Spring Boot 4.x

Closes gh-47916

documentation/spring-boot-docs/src/docs/antora/modules/ROOT/pages/documentation.adoc

@@ -27,6 +27,7 @@ Depending on the version that you are upgrading to, you can find some additional
 
 * *From 1.x to 2.x:* xref:upgrading.adoc#upgrading.from-1x[Upgrading from 1.x]
 * *From 2.x:* xref:upgrading.adoc#upgrading.from-2x[Upgrading from 2.x]
+* *From 3.x:* xref:upgrading.adoc#upgrading.from-3x[Upgrading from 3.x]
 * *To a new feature release:* xref:upgrading.adoc#upgrading.to-feature[Upgrading to New Feature Release]
 * *Spring Boot CLI:* xref:upgrading.adoc#upgrading.cli[Upgrading the Spring Boot CLI]
 

documentation/spring-boot-docs/src/docs/antora/modules/ROOT/pages/upgrading.adoc

@@ -13,7 +13,7 @@ If you are more than one release behind, please make sure that you also review t
 == Upgrading From 1.x
 
 If you are upgrading from the `1.x` release of Spring Boot, check the {url-github-wiki}/Spring-Boot-2.0-Migration-Guide[migration guide] on the project wiki that provides detailed upgrade instructions to upgrade to Spring Boot 2.x.
-Check also the {url-github-wiki}[release notes] for a list of "`new and noteworthy`" features for each release.
+Check also the {url-github-wiki}#release-notes[release notes] for a list of "`new and noteworthy`" features for each release.
 
 
 
@@ -21,7 +21,15 @@ Check also the {url-github-wiki}[release notes] for a list of "`new and notewort
 == Upgrading From 2.x
 
 If you are upgrading from the `2.x` release of Spring Boot, check the {url-github-wiki}/Spring-Boot-3.0-Migration-Guide[migration guide] on the project wiki that provides detailed upgrade instructions.
-Check also the {url-github-wiki}[release notes] for a list of "`new and noteworthy`" features for each release.
+Check also the {url-github-wiki}#release-notes[release notes] for a list of "`new and noteworthy`" features for each release.
+
+
+
+[[upgrading.from-3x]]
+== Upgrading From 3.x
+
+If you are upgrading from the `3.x` release of Spring Boot, check the {url-github-wiki}/Spring-Boot-4.0-Migration-Guide[migration guide] on the project wiki that provides detailed upgrade instructions.
+Check also the {url-github-wiki}#release-notes[release notes] for a list of "`new and noteworthy`" features for each release.