Replace matrix.domain with matrix.example.com

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

docs/configuring-playbook-bot-postmoogle.md

@@ -71,7 +71,7 @@ ansible-playbook -i inventory/hosts setup.yml --tags=setup-all,ensure-matrix-use
 
 To use the bot, invite the `@postmoogle:example.com` bot user into a room you want to use as a mailbox.
 
-Then send `!pm mailbox NAME` to expose this Matrix room as an inbox with the email address `NAME@matrix.domain`. Emails sent to that email address will be forwarded to the room.
+Then send `!pm mailbox NAME` to expose this Matrix room as an inbox with the email address `NAME@matrix.example.com`. Emails sent to that email address will be forwarded to the room.
 
 Send `!pm help` to the room to see the bot's help menu for additional commands.