fix(docs): Mark set_ssl_acceptor doctest no_run

The example builds an SslAcceptor by calling openssl's
set_private_key_file/set_certificate_file, which open the files at test
time. CI doesn't have those PEM files, so the doctest panicked.

Locally it passed only because gitignored windmark_private.pem and
windmark_public.pem were left in the working tree.

Author: Fuwn

src/router.rs

@@ -660,7 +660,7 @@ impl Router {
   ///
   /// # Examples
   ///
-  /// ```rust
+  /// ```rust,no_run
   /// use openssl::ssl;
   ///
   /// windmark::router::Router::new().set_ssl_acceptor({