clarify why partial examples are not encouraged

Author: nbogie

contributor_docs/contributing_to_the_p5js_reference.md

@@ -747,7 +747,7 @@ We won’t go through the details about best practices and code style for the ex
 
 ### When examples omit setup()
 
-If the `setup()` function is not included, such as in the example above, the code will be automatically wrapped in a `setup()` function with a default 100x100 pixels gray background canvas created.  While you will see such examples included in this guide for brevity, it is generally preferred that your example be a complete sketch.
+If the `setup()` function is not included, such as in the example above, the code will be automatically wrapped in a `setup()` function with a default 100x100 pixels gray background canvas created.  While you may see such examples included in this guide for brevity, it is generally preferred that your example be a complete sketch.  This makes it easier for learners to see the intended usage in full context and copy-paste to get a complete runnable example in their own editor.
 
 ### <a id="norender"></a>Preventing execution of example code with `norender`