HPCC-8955 Document changes to "packagemap validate"

Signed-off-by: JamesDeFabia <James.Defabia@LexisNexis.com>
Merge pull request #4158 from JamesDeFabia/DocumentChanges_to_packagemap_validate8955

HPCC-8955 Document changes to "packagemap validate"

Reviewed-By: Anthony Fishbeck <anthony.fishbeck@lexisnexis.com>
Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>