Add a paragraph about how to force a stack trace dump to the daemon log. This feature was added in Docker 1.9 I believe, but documentation was never added. Docker-DCO-1.1-Signed-off-by: Phil Estes <estesp@linux.vnet.ibm.com> (github: estesp) Upstream-commit: ae466aafcbd3e000ff9ec2e8bd354fc3cc3729e5 Component: engine