update obmc-host-start target link

The targets were recently moved into phosphor-state-manager so link
needs to be updated

Change-Id: I571aa1c7674d75657c7d9426dcc8b70ffafaf78b
Signed-off-by: Andrew Geissler <geissonator@yahoo.com>
diff --git a/architecture/openbmc-systemd.md b/architecture/openbmc-systemd.md
index 6713fee..9572e05 100644
--- a/architecture/openbmc-systemd.md
+++ b/architecture/openbmc-systemd.md
@@ -33,7 +33,7 @@
 You'll find all the phosphor services associated with multi-user.target.
 
 ## Server Power On
-When OpenBMC is used within a server, the [obmc-host-start@.target](https://github.com/openbmc/openbmc/blob/171031d20c7ed03900739d51ba53ad0001f98fa5/meta-phosphor/common/recipes-core/systemd/obmc-targets/obmc-host-start%40.target)
+When OpenBMC is used within a server, the [obmc-host-start@.target](https://github.com/openbmc/phosphor-state-manager/blob/master/target_files/obmc-host-start%40.target)
 is what drives the boot of the system.
 
 If you dig into its .requires relationship, you'll see the following in the file