[MINOR][PYSPARK] Improve error message when running PySpark with different minor versions

## What changes were proposed in this pull request?

Currently the error message is correct but doesn't provide additional hint to new users. It would be better to hint related configuration to users in the message.

## How was this patch tested?

N/A because it only changes error message.

Please review https://cwiki.apache.org/confluence/display/SPARK/Contributing+to+Spark before opening a pull request.

Author: Liang-Chi Hsieh <viirya@gmail.com>

Closes #15822 from viirya/minor-pyspark-worker-errmsg.

python/pyspark/worker.py

@@ -119,7 +119,9 @@ def main(infile, outfile):
         version = utf8_deserializer.loads(infile)
         if version != "%d.%d" % sys.version_info[:2]:
             raise Exception(("Python in worker has different version %s than that in " +
-                             "driver %s, PySpark cannot run with different minor versions") %
+                             "driver %s, PySpark cannot run with different minor versions." +
+                             "Please check environment variables PYSPARK_PYTHON and " +
+                             "PYSPARK_DRIVER_PYTHON are correctly set.") %
                             ("%d.%d" % sys.version_info[:2], version))
 
         # initialize global state