[SPARK-32677][SQL][DOCS][MINOR] Improve code comment in CreateFunctio…

…nCommand

### What changes were proposed in this pull request?

We made a mistake in #29502, as there is no code comment to explain why we can't load the UDF class when creating functions. This PR improves the code comment.

### Why are the changes needed?

To avoid making the same mistake.

### Does this PR introduce _any_ user-facing change?

No

### How was this patch tested?

N/A

Closes #29713 from cloud-fan/comment.

Authored-by: Wenchen Fan <wenchen@databricks.com>
Signed-off-by: Takeshi Yamamuro <yamamuro@apache.org>

sql/core/src/main/scala/org/apache/spark/sql/execution/command/functions.scala

@@ -88,7 +88,9 @@ case class CreateFunctionCommand(
       } else {
         // For a permanent, we will store the metadata into underlying external catalog.
         // This function will be loaded into the FunctionRegistry when a query uses it.
-        // We do not load it into FunctionRegistry right now.
+        // We do not load it into FunctionRegistry right now, to avoid loading the resource and
+        // UDF class immediately, as the Spark application to create the function may not have
+        // access to the resource and/or UDF class.
         catalog.createFunction(func, ignoreIfExists)
       }
     }