docs: Update custom_diagram docs

Co-authored-by: Martin Lehmann <[email protected]>

docs/custom_diagram.md

@@ -5,7 +5,8 @@
 
 # Custom Diagram
 
-`Custom diagram`s let's you create custom diagrams based on the data in the model. You define the data collection using an iterable and `Custom diagram` takes care of the rest.
+`Custom diagram`s let you create custom diagrams based on the data in the model. You define the data collection using an iterable, and `Custom diagram` takes care of the rest.
+
 You can access `.custom_diagram` on any supported model element.
 
 ??? example "Custom Diagram of `PP 1 `"