Update upgrade guide

Author: Flo0807

guides/upgrading/v0.15.md

@@ -55,9 +55,31 @@ use Backpex.LiveResource,
   layout: &MyAppWeb.admin/1
 ```
 
-## Resource.update/6 has been changed
+## Resource and adapter functions have been updated
 
-We no longer pass the `fields` to `Resource.update/6`. Therefore, the arity of this functions has changed to `Backpex.Resource.update/5`. This aligns the function `insert` and `update` of the Resource module.
+We've updated some functions in `Backpex.Resource` and the adapter modules (`Backpex.Adapters.Ecto` and `Backpex.Adapters.Ash`) to include the fields as an additional parameter.
+
+The following functions are affected:
+
+`Backpex.Resource`:
+- `list/3` -> `Backpex.Resource.list/4`
+- `count/3` -> `Backpex.Resource.count/4`
+- `get/3` -> `Backpex.Resource.get/4`
+- `get!/3` -> `Backpex.Resource.get!/4`
+
+`Backpex.Adapter` (including `Backpex.Adapters.Ecto` and `Backpex.Adapters.Ash`):
+- `list/3` -> `c:Backpex.Adapter.list/4`
+- `count/3` -> `c:Backpex.Adapter.count/4`
+- `get/3` -> `c:Backpex.Adapter.get/4`
+
+For example:
+
+```elixir
+# before
+Resource.get(primary_value, socket.assigns, live_resource)
+# after
+Resource.get(primary_value, fields, socket.assigns, live_resource)
+```
 
 ## `:only`/`:except` field option changes