[DOCS] Added a note in impala_scan_bytes_limit.xml
[DOCS] Added a note in impala_scan_bytes_limit.xml

- Added a note that queries can scan over the limit of this option
at times.

Change-Id: Id20f952622ce553d9c1f47e469d97a3b4c19683f
Reviewed-on: http://gerrit.cloudera.org:8080/11936
Tested-by: Impala Public Jenkins <039b6b20426ff68ebe492b3021890d8c8fd010c9@cloudera.com>
Reviewed-by: Bikramjeet Vig <f534d302728ba886c91adfa78952ab96e2b2b265@cloudera.com>

cloudera/Impala,cloudera/Impala,cloudera/Impala,cloudera/Impala,cloudera/Impala,cloudera/Impala,cloudera/Impala