Using pi.hole as hostname

To be consistent with the parameter already defined in docker_run.sh
(leaving the jwilder-proxy example to pihole.yourDomain.lan to be 
consistent with the rest of that file's content, namely DEFAULT_HOST)

README.md

@@ -18,7 +18,7 @@ services:
   pihole:
     container_name: pihole
     image: pihole/pihole:latest
-    hostname: pihole
+    hostname: pi.hole
     ports:
       - "53:53/tcp"
       - "53:53/udp"

docker-compose.yml.example

@@ -6,7 +6,7 @@ services:
   pihole:
     container_name: pihole
     image: pihole/pihole:latest
-    hostname: pihole
+    hostname: pi.hole
     # For DHCP it is recommended to remove these ports and instead add: network_mode: "host"
     ports:
       - "53:53/tcp"