Improve local dev override docs and add read-only example

examples/read_only/main.tf

@@ -0,0 +1,12 @@
+# Lists all Dynu domains available to the configured API key.
+data "dynu_domains" "all" {}
+
+# Resolves the Dynu root domain for a specific hostname.
+data "dynu_domain" "selected" {
+  hostname = var.hostname
+}
+
+# Lists DNS records for the root domain resolved from the same hostname.
+data "dynu_dns_records" "selected" {
+  hostname = var.hostname
+}