Clarified help text for link_id to indicate alphanumeric characters are meant.
Clarified help text for link_id to indicate alphanumeric characters are meant.

Fixes Issue 746.

SRabbelier/Melange,SRabbelier/Melange,SRabbelier/Melange,SRabbelier/Melange,SRabbelier/Melange,SRabbelier/Melange,SRabbelier/Melange,SRabbelier/Melange,SRabbelier/Melange