Update documentation about hooks depreciation

Signed-off-by: Feruzjon Muyassarov <[email protected]>

docs/advanced/customization-guide.md

@@ -153,6 +153,16 @@ should be placed in a separate directory in order to avoid NFD unnecessarily
 trying to execute them. A subdirectory under the hooks directory can be used,
 for example `/etc/kubernetes/node-feature-discovery/source.d/conf/`.
 
+**NOTE:** Hooks are being DEPRECATED and will be removed in the future releases.
+For backward compatibility, currently hooks are enabled by default and can be
+disabled via `sources.local.hooksEnabled` field in the worker configuration.
+
+```yaml
+sources:
+  local:
+    hooksEnabled: true  # true by default at this point
+```
+
 **NOTE:** NFD will blindly run any executables placed/mounted in the hooks
 directory. It is the user's responsibility to review the hooks for e.g.
 possible security implications.