doc/radosgw: multisite - edit "migrating a single-site"

Add the import step of the section "Migrating a Single-Site Deployment to Multi-Site"
in doc/radosgw/multisite.rst. The field "name" and "api_name" should be matched.

Signed-off-by: Qi Tao <[email protected]>

Author: tgfree7

doc/radosgw/multisite.rst

@@ -751,15 +751,21 @@ to a multi-site system, follow these steps:
       radosgw-admin zonegroup rename --rgw-zonegroup default --zonegroup-new-name=<name>
       radosgw-admin zone rename --rgw-zone default --zone-new-name us-east-1 --rgw-zonegroup=<name>
 
-3. Configure the master zonegroup. Replace ``<name>`` with the realm name or
+3. Rename the default zonegroup's ``api_name``. Replace ``<name>`` with the zonegroup name:
+
+   .. prompt:: bash #
+
+      radosgw-admin zonegroup modify --api-name=<name> --rgw-zonegroup=<name>
+
+4. Configure the master zonegroup. Replace ``<name>`` with the realm name or
    zonegroup name. Replace ``<fqdn>`` with the fully qualified domain name(s)
    in the zonegroup:
 
    .. prompt:: bash #
 
       radosgw-admin zonegroup modify --rgw-realm=<name> --rgw-zonegroup=<name> --endpoints http://<fqdn>:80 --master --default
 
-4. Configure the master zone. Replace ``<name>`` with the realm name, zone
+5. Configure the master zone. Replace ``<name>`` with the realm name, zone
    name, or zonegroup name. Replace ``<fqdn>`` with the fully qualified domain
    name(s) in the zonegroup:
 
@@ -770,7 +776,7 @@ to a multi-site system, follow these steps:
                                 --access-key=<access-key> --secret=<secret-key> \
                                 --master --default
 
-5. Create a system user. Replace ``<user-id>`` with the username.  Replace
+6. Create a system user. Replace ``<user-id>`` with the username.  Replace
    ``<display-name>`` with a display name. The display name is allowed to
    contain spaces:
 
@@ -781,13 +787,13 @@ to a multi-site system, follow these steps:
       --access-key=<access-key> \ 
       --secret=<secret-key> --system
 
-6. Commit the updated configuration:
+7. Commit the updated configuration:
 
    .. prompt:: bash #
 
       radosgw-admin period update --commit
 
-7. Restart the Ceph Object Gateway:
+8. Restart the Ceph Object Gateway:
 
    .. prompt:: bash #