add example file for secrets

secrets.nix.example

@@ -0,0 +1,23 @@
+{
+  aria2_config = {
+    rpc_secret = "<rpc secret for aria2>";
+  };
+  frp_config = {
+    ip = "<ip addess of server running frps>";
+    token = "<secret token for frps <-> frpc connection>";
+  };
+  caddy_config = {
+    email = "<email for certificate generation>";
+  };
+  users = {
+    root.hashedPassword = "<password hash of root user>";
+    primary = {
+      userName = "<primary non-root username>";
+      realName = "<primary user's full name>";
+      hashedPassword = "<password hash of primary user>";
+      pgpFingerprint = "<primary user's pgp fingerprint>";
+      emailAddress = "<primary user's email>";
+      sshPublicKey = "<ssh public key>";
+    };
+  };
+}