HOWTO: Add the knwon_regression URI to the documentation

We should let everybody know about where the regression
list is hosted. The more is known the more it is used.

Signed-off-by: Paolo Ciarrocchi <paolo.ciarrocchi@gmail.com>
Cc: Li Yang <leoli@freescale.com>
Cc: TripleX Chung <xxx.phy@gmail.com>
Cc: Maggie Chen <chenqi@beyondsoft.com>
Cc: WANG Cong <xiyou.wangcong@gmail.com>
Cc: Tsugikazu Shibata <tshibata@ab.jp.nec.com>
Cc: IKEDA Munehiro <m-ikeda@ds.jp.nec.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>