update README examples to use transfer plugins (#4163)

Signed-off-by: Chris O'Haver <cohaver@infoblox.com>

README.md

@@ -27,7 +27,7 @@ Currently CoreDNS is able to:
 * Retrieve zone data from primaries, i.e., act as a secondary server (AXFR only) (*secondary*).
 * Sign zone data on-the-fly (*dnssec*).
 * Load balancing of responses (*loadbalance*).
-* Allow for zone transfers, i.e., act as a primary server (*file*).
+* Allow for zone transfers, i.e., act as a primary server (*file* + *transfer*).
 * Automatically load zone files from disk (*auto*).
 * Caching of DNS responses (*cache*).
 * Use etcd as a backend (replacing [SkyDNS](https://github.com/skynetservices/skydns)) (*etcd*).
@@ -137,9 +137,9 @@ send notifies to it.
 
 ~~~ txt
 example.org:1053 {
-    file /var/lib/coredns/example.org.signed {
-        transfer to *
-        transfer to 2001:500:8f::53
+    file /var/lib/coredns/example.org.signed
+    transfer {
+        to * 2001:500:8f::53
     }
     errors
     log
@@ -151,9 +151,9 @@ recursive nameserver *and* rewrite ANY queries to HINFO.
 
 ~~~ txt
 example.org:1053 {
-    file /var/lib/coredns/example.org.signed {
-        transfer to *
-        transfer to 2001:500:8f::53
+    file /var/lib/coredns/example.org.signed
+    transfer {
+        to * 2001:500:8f::53
     }
     errors
     log