update doc to not use the root zone for everything (#3288)

Update all documentation in the tree to use example.org as an example
configuration (in so far possible). As to get out of the just use "."
and fallthrough and things would be fine.

Signed-off-by: Miek Gieben <miek@miek.nl>

plugin/cancel/README.md

@@ -25,7 +25,7 @@ cancel [TIMEOUT]
 ## Examples
 
 ~~~ corefile
-. {
+example.org {
     cancel
     whoami
 }
@@ -34,7 +34,7 @@ cancel [TIMEOUT]
 Or with a custom timeout:
 
 ~~~ corefile
-. {
+example.org {
     cancel 1s
     whoami
 }