HPCC-11951 Update docs to say Roxie can write files

Signed-off-by: Jim DeFabia <jamesdefabia@lexisnexis.com>
Merge pull request #6750 from JamesDeFabia/roxiewrites

HPCC-11951 Update docs to say Roxie can write files

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>