CURLOPT_USERAGENT.3: added an example

docs/libcurl/opts/CURLOPT_USERAGENT.3

@@ -5,7 +5,7 @@
 .\" *                            | (__| |_| |  _ <| |___
 .\" *                             \___|\___/|_| \_\_____|
 .\" *
-.\" * Copyright (C) 1998 - 2014, Daniel Stenberg, <daniel@haxx.se>, et al.
+.\" * Copyright (C) 1998 - 2015, Daniel Stenberg, <daniel@haxx.se>, et al.
 .\" *
 .\" * This software is licensed as described in the file COPYING, which
 .\" * you should have received as part of this distribution. The terms
@@ -37,7 +37,16 @@ NULL, no User-Agent: header is used by default.
 .SH PROTOCOLS
 HTTP, HTTPS
 .SH EXAMPLE
-TODO
+.nf
+CURL *curl = curl_easy_init();
+if(curl) {
+  curl_easy_setopt(curl, CURLOPT_URL, "http://example.com");
+
+  curl_easy_setopt(curl, CURLOPT_USERAGENT, "Dark Secret Ninja/1.0");
+
+  curl_easy_perform(curl);
+}
+.fi
 .SH AVAILABILITY
 As long as HTTP is supported
 .SH RETURN VALUE