A new documentation is available for Squash TM 2.0 and later versions, check it here
This article explains how the Xsquash plugin works together with JIRA.
9.01 - Introduction
9.02 - Synchronized requirements
9.03 - The target directory
9.04 - Agile Scrum tables synchronization
9.05 - Other types of synchronization
9.06 - Sub-tasks
9.07 - Hybrid hierarchy