add acme contact

idk if this helps rate-limiting, prob not

slingshot/src/main.rs

···
     /// - TODO: a rate-limiter will be installed
     #[arg(long)]
     host: Option<String>,
+    /// email address for letsencrypt contact
+    ///
+    /// recommended in production, i guess?
+    #[arg(long)]
+    acme_contact: Option<String>,
     /// a location to cache acme https certs
     ///
     /// only used if --host is specified. omitting requires re-requesting certs
···
             identity,
             repo,
             args.host,
+            args.acme_contact,
             args.certs,
             server_shutdown,
         )

slingshot/src/server.rs

···
     identity: Identity,
     repo: Repo,
     host: Option<String>,
+    acme_contact: Option<String>,
     certs: Option<PathBuf>,
     _shutdown: CancellationToken,
 ) -> Result<(), ServerError> {
···
         let mut auto_cert = AutoCert::builder()
             .directory_url(LETS_ENCRYPT_PRODUCTION)
             .domain(&host);
+        if let Some(contact) = acme_contact {
+            auto_cert = auto_cert.contact(contact);
+        }
         if let Some(certs) = certs {
-            auto_cert = auto_cert.cache_path(certs)
+            auto_cert = auto_cert.cache_path(certs);
         }
         let auto_cert = auto_cert.build().map_err(ServerError::AcmeBuildError)?;