Update REST-cheatsheet.md documentation

Added:
   - Updating default "root" password.

Change-Id: Icdb4994f8f9f241649dc797cb654790e7dc71830
Signed-off-by: George Keishing <gkeishin@in.ibm.com>
diff --git a/REST-cheatsheet.md b/REST-cheatsheet.md
index f04187b..847a6c9 100644
--- a/REST-cheatsheet.md
+++ b/REST-cheatsheet.md
@@ -129,3 +129,11 @@
     $ curl -c cjar -b cjar -k -H "Content-Type: application/json" -X PUT https://${bmc}/xyz/openbmc_project/control/power_supply_redundancy/attr/PowerSupplyRedundancyEnabled -d '{"data": 1}'
     $ curl -c cjar -b cjar -k -H "Content-Type: application/json" -X PUT https://${bmc}/xyz/openbmc_project/control/power_supply_redundancy/attr/PowerSupplyRedundancyEnabled -d '{"data": 0}'
     ```
+
+* Update "root" password:
+
+    - Change password from "OpenBmc" to "abc123":
+    ```
+    $ curl -c cjar -b cjar -k -H "Content-Type: application/json" -X POST https://${bmc}/login -d "{\"data\": [ \"root\", \"0penBmc\" ] }"
+    $ curl -c cjar -b cjar -k -H "Content-Type: application/json" -d "{\"data\": [\"abc123\"] }" -X POST  https://${bmc}/xyz/openbmc_project/user/root/action/SetPassword
+    ```