Add v15 breaking changes section

Author: nikolajlauridsen

15/umbraco-cms/fundamentals/setup/upgrading/version-specific/README.md

@@ -19,6 +19,19 @@ Use the [general upgrade guide](../) to complete the upgrade of your project.
 
 <details>
 
+<summary>Umbraco 15</summary>
+
+* **Snapshots are removed**
+
+Snapshots has been removed, this means that any code that used `IPublishedSnapshot`, and by extension `IPublishedSnapshotAccessor`, must be updated. The specific changes depends on the use case of the snapshot, in most cases it can be solved by instead injecting `IPublishedContentCache` or `IPublishedMediaCache` and using those directly.
+
+* **Modelsbuilder models needs to be rebuilt**
+
+Models generated by ModelsBuilder used the `IPublishedSnapshot` interface, which has been removed. This means that the models needs to be rebuilt, the approach to this will differ on the models mode chosen:
+
+* InMemoryAuto - Remove the `umbraco\Data\TEMP\InMemoryAuto` folder, this will trigger a rebuild of the models.
+* SourceCodeAuto and SourceCodeManual - Remove the old models, by default these are located in the `\umbraco\models` folder, and then trigger a rebuild of the models from the dashboard in the backoffice.
+
 <summary>Umbraco 14</summary>
 
 Read more about the release of Umbraco 14 in the [Blog Post](https://umbraco.com/blog/umbraco-14-release/).
@@ -952,7 +965,7 @@ Task<bool> TryFindContent(IPublishedRequestBuilder request);
 [**Async tree search**](https://github.com/umbraco/Umbraco-CMS/pull/12344)
 
 ```CSharp
-IEnumerable<SearchResultEntity?> Search(string query, int pageSize, long pageIndex, out long totalFound, string? searchFrom 
+IEnumerable<SearchResultEntity?> Search(string query, int pageSize, long pageIndex, out long totalFound, string? searchFrom
 = null)
 ```
 
@@ -996,7 +1009,7 @@ In the `_ViewImports.cshtml` of your project, remove the following lines:
 
 ```
 @addTagHelper *, Smidge
-@inject Smidge.SmidgeHelper SmidgeHelper 
+@inject Smidge.SmidgeHelper SmidgeHelper
 ```
 
 Otherwise, it will cause an error on the front end.