Add example module for documentation

It currently doesn't show anything as all items are pub(crate).

src/example.rs

@@ -0,0 +1,35 @@
+//! This module demonstrate what a `config!` invocation will generate. This
+//! module exists merely for documentation purposes and is not usable from your
+//! crate.
+//!
+//! TODO
+
+use std::{net::IpAddr, path::PathBuf};
+
+// This is necessary because the macro generates a bunch of paths starting with
+// `confique`, assuming that symbol is in scope.
+#[doc(hidden)]
+use crate as confique;
+
+crate::config! {
+    dns: {
+        /// The DNS server IP address.
+        #[example = "1.1.1.1"]
+        server: IpAddr,
+
+        /// Whether to use a local DNS resolution cache.
+        use_cache: bool = true,
+
+        /// How often to reattempt reaching the DNS server.
+        retry_attempts: u32 = 27,
+    },
+    log: {
+        /// Sets the log level. Possible values: "trace", "debug", "info",
+        /// "warn", "error" and "off".
+        level: log::LevelFilter = "info",
+
+        /// If this is set, log messages are also written to this file.
+        #[example = "/var/log/test.log"]
+        file: Option<PathBuf>,
+    },
+}