Add example for using Postgres

examples/docker-compose-postgres-storage/config.yaml

@@ -0,0 +1,42 @@
+storage:
+  type: postgres
+  file: "postgres://username:password@postgres:5432/gatus?sslmode=disable"
+
+services:
+  - name: back-end
+    group: core
+    url: "https://example.org/"
+    interval: 5m
+    conditions:
+      - "[STATUS] == 200"
+      - "[CERTIFICATE_EXPIRATION] > 48h"
+
+  - name: monitoring
+    group: internal
+    url: "https://example.org/"
+    interval: 5m
+    conditions:
+      - "[STATUS] == 200"
+
+  - name: nas
+    group: internal
+    url: "https://example.org/"
+    interval: 5m
+    conditions:
+      - "[STATUS] == 200"
+
+  - name: example-dns-query
+    url: "8.8.8.8" # Address of the DNS server to use
+    interval: 5m
+    dns:
+      query-name: "example.com"
+      query-type: "A"
+    conditions:
+      - "[BODY] == 93.184.216.34"
+      - "[DNS_RCODE] == NOERROR"
+
+  - name: icmp-ping
+    url: "icmp://example.org"
+    interval: 1m
+    conditions:
+      - "[CONNECTED] == true"