rest-api: Add warning about default disabled

https://github.com/openbmc/phosphor-rest-server has been archived which
leaves bmcweb as the only actively developed webserver in OpenBMC. The
OpenBMC REST API is disabled by default in bmcweb and has been for a
year+.

Was very soft with the wording here, could use stronger language like
OPENBMC REST being deprecated or unsupported. Could also add -deprecated
to the filenames and move these. Changes for the future.

Tested: Pushed to my fork and looks good.

Change-Id: I693064885c1ba7ea6c3ca7d3381e7c638dbc6649
Signed-off-by: Gunnar Mills <[email protected]>

Author: gtmills

rest-api.md

@@ -1,7 +1,8 @@
 # OpenBMC REST API
 
-The primary management interface for OpenBMC is REST. This document provides
-some basic structure and usage examples for the REST interface.
+The OpenBMC REST API is disabled by default in bmcweb. Most of the functionality
+is available on Redfish. This document provides some basic structure and usage
+examples for the OpenBMC REST interface.
 
 The schema for the rest interface is directly defined by the OpenBMC D-Bus
 structure. Therefore, the objects, attributes and methods closely map to those