Add README to export_to_cluster
Add README to export_to_cluster

Fix https://github.com/TGAC/earlham-galaxytools/issues/87 .

anilthanki/tgac-galaxytools,TGAC/earlham-galaxytools,TGAC/earlham-galaxytools,TGAC/earlham-galaxytools,TGAC/earlham-galaxytools,anilthanki/tgac-galaxytools,TGAC/tgac-galaxytools,anilthanki/tgac-galaxytools,anilthanki/tgac-galaxytools,anilthanki/tgac-galaxytools,TGAC/tgac-galaxytools,TGAC/earlham-galaxytools