Added documentation for the core module

docs/Writerside/topics/Callbacks.md

@@ -1,3 +1,31 @@
 # Callbacks
 
-Start typing here...
+Callbacks are a way of executing actions on curtain events in the web ui.
+
+## Registering a callback handler
+
+You can register a callback handler using the method provided in the [](TableConfig.md):
+
+```c#
+table.AddCallbackHandler(CallbackType.DeleteEntry, (user, services) => {
+    var logger = services.GetRequiredService<ILogger<Program>>();
+    logger.LogInformation("User {user} deleted!", user.Username);
+});
+```
+
+The callback handler takes the entity that's modified and a `IServiceProvider` as arguments
+and can either be synchronous or asynchronous.
+
+## Callback types
+
+```C#
+public enum CallbackType {
+    CreateEntry = 0,
+    UpdateEntry = 1,
+    DeleteEntry = 2
+}
+```
+
+- `CallbackType.CreateEntry`: The handler gets executed, when an entity is created.
+- `CallbackType.UpdateEntry`: The handler gets executed, when an entity is updated.
+- `CallbackType.DeleteEntry`: The handler gets executed, when an entity is deleted.