chore(lambda): improve tsdoc for handler property (aws#5338)

packages/@aws-cdk/aws-lambda/lib/function.ts

@@ -49,9 +49,10 @@ export interface FunctionProps {
   readonly description?: string;
 
   /**
-   * The name of the function (within your source code) that Lambda calls to
-   * start running your code. For more information, see the Handler property
-   * in the AWS Lambda Developer Guide.
+   * The name of the method within your code that Lambda calls to execute
+   * your function. The format includes the file name. It can also include
+   * namespaces and other qualifiers, depending on the runtime.
+   * For more information, see https://docs.aws.amazon.com/lambda/latest/dg/gettingstarted-features.html#gettingstarted-features-programmingmodel.
    *
    * NOTE: If you specify your source code as inline text by specifying the
    * ZipFile property within the Code property, specify index.function_name as