Update README.md

Add link to Sling Models documentation
diff --git a/README.md b/README.md
index b231ed2..3c984d5 100644
--- a/README.md
+++ b/README.md
@@ -7,3 +7,5 @@
 This module is part of the [Apache Sling](https://sling.apache.org) project.
 This bnd plugin detects all Sling Models classes and adds a `Sling-Model-Classes` bundle header to the bundle being built, containing the model class names.
+Usage is described in [Sling Models](https://sling.apache.org/documentation/bundles/models.html#registration-of-sling-models-classes-via-bnd-plugin).