power-recovery: Add Content-Type

From https://www.w3.org/Protocols/rfc2616/rfc2616-sec7.html#sec7.2.1:
Any HTTP/1.1 message containing an entity-body SHOULD include a
Content-Type header field defining the media type of that body.

Redfish also mentions this "In HTTP messages, the media type is
specified in the Content-Type header."

bmcweb is attempting to validate content-type header,
https://gerrit.openbmc.org/c/openbmc/bmcweb/+/59941.

Change-Id: Ie020df1fd3b46ba1dad9720be5c8b384a77d7d7e
Signed-off-by: Gunnar Mills <gmills@us.ibm.com>
diff --git a/designs/power-recovery.md b/designs/power-recovery.md
index e3fe7a8..3465b0d 100644
--- a/designs/power-recovery.md
+++ b/designs/power-recovery.md
@@ -290,9 +290,9 @@
 
 ```
 #  Power Restore Policy
-curl -k -X PATCH -d '{"PowerRestorePolicy":"AlwaysOn"}' https://${bmc}/redfish/v1/Systems/system
-curl -k -X PATCH -d '{"PowerRestorePolicy":"AlwaysOff"}' https://${bmc}/redfish/v1/Systems/system
-curl -k -X PATCH -d '{"PowerRestorePolicy":"LastState"}' https://${bmc}/redfish/v1/Systems/system
+curl -k -H "Content-Type: application/json" -X PATCH -d '{"PowerRestorePolicy":"AlwaysOn"}' https://${bmc}/redfish/v1/Systems/system
+curl -k -H "Content-Type: application/json" -X PATCH -d '{"PowerRestorePolicy":"AlwaysOff"}' https://${bmc}/redfish/v1/Systems/system
+curl -k -H "Content-Type: application/json" -X PATCH -d '{"PowerRestorePolicy":"LastState"}' https://${bmc}/redfish/v1/Systems/system
 ```
 
 For testing, each policy should be set and verified. The one_time aspect should