Correct inconsistent indentation

the contents of `volumes` was indented an extra space.

Signed-off-by: Daniel Hoherd <daniel.hoherd@gmail.com>

README.md

@@ -28,8 +28,8 @@ services:
       # WEBPASSWORD: 'set a secure password here or it will be random'
     # Volumes store your data between container upgrades
     volumes:
-       - './etc-pihole/:/etc/pihole/'
-       - './etc-dnsmasq.d/:/etc/dnsmasq.d/'
+      - './etc-pihole/:/etc/pihole/'
+      - './etc-dnsmasq.d/:/etc/dnsmasq.d/'
     dns:
       - 127.0.0.1
       - 1.1.1.1