HPCC-10140 Document Virtual Logicalfilename

Signed-off-by: JamesDeFabia <James.Defabia@LexisNexis.com>
HPCC-10140 Edits based on code review

Signed-off-by: JamesDeFabia <James.Defabia@LexisNexis.com>
Merge pull request #5001 from JamesDeFabia/10140DocumentVirtualLogicalFileName

HPCC-10140 Document Virtual Logicalfilename

Reviewed-by: Gavin Halliday <ghalliday@hpccsystems.com>