update documentation on clearing of *-on files

See previous commits in this series for the reasoning behind this.

TLDR: Clearing them on the power off paths caused complexity with other
paths like BMC resets with the host up and warm reboots.

Signed-off-by: Andrew Geissler <geissonator@yahoo.com>
Change-Id: I78e8894238538c11f12b287fa8fe34858f0abff4
diff --git a/README.md b/README.md
index 4ae1966..1478639 100644
--- a/README.md
+++ b/README.md
@@ -107,7 +107,9 @@
     correctly report that the chassis is `On`
 - Start a service to check if the host is on
 
-The chassis@0-on file is removed when power is removed from the chassis.
+The chassis@0-on file is removed once the obmc-chassis-poweron@0.target becomes
+active (i.e. all service have been successfully started which are wanted or
+required by this target).
 
 The logic to check if the host is on sends a command to the host, and if a
 response is received then similar logic to chassis is done:
@@ -117,7 +119,9 @@
     and their service files implementing a
     "ConditionPathExists=!/run/openbmc/host@0-request"
 
-The host@0-on file is removed when the host is stopped.
+The host@0-on file is removed once the obmc-host-start@0.target and
+obmc-host-startmin@0.target become active (i.e. all service have been
+successfully started which are wanted or required by these targets).
 
 ## Building the Code
 ```