mention default port number

docs/libcurl/curl_easy_setopt.3

@@ -445,7 +445,8 @@ Set HTTP proxy to use. The parameter should be a char * to a zero terminated
 string holding the host name or dotted IP address. To specify port number in
 this string, append :[port] to the end of the host name. The proxy string may
 be prefixed with [protocol]:// since any such prefix will be ignored. The
-proxy's port number may optionally be specified with the separate option
+proxy's port number may optionally be specified with the separate option. If
+not specified, libcurl will default to using port 1080 for proxies.
 \fICURLOPT_PROXYPORT\fP.
 
 When you tell the library to use an HTTP proxy, libcurl will transparently