[SPARK-3035] Wrong example with SparkContext.addFile

https://issues.apache.org/jira/browse/SPARK-3035

fix for wrong document.

Author: iAmGhost <kdh7807@gmail.com>

Closes #1942 from iAmGhost/master and squashes the following commits:

487528a [iAmGhost] [SPARK-3035] Wrong example with SparkContext.addFile fix for wrong document.

(cherry picked from commit 379e7585c356f20bf8b4878ecba9401e2195da12)
Signed-off-by: Josh Rosen <joshrosen@apache.org>