[SCSI] scsi: Error handler description document

This patch adds Documentation/scsi/scs_eh.txt.  I've chosen plain
text over DocBook as most other scsi docs are in plain text and it's
more accessible.
Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>

Documentation/scsi/00-INDEX

@@ -60,6 +60,8 @@ scsi.txt
 	- short blurb on using SCSI support as a module.
 scsi_mid_low_api.txt
 	- info on API between SCSI layer and low level drivers
+scsi_eh.txt
+	- info on SCSI midlayer error handling infrastructure
 st.txt
 	- info on scsi tape driver
 sym53c500_cs.txt