Merge pull request #2901 from matteob8/patch-1

Update http_server.pl

src/lib/http/http_server.pl

@@ -17,6 +17,8 @@ as one HTTP method (in lowercase) and followed by a Route Match and a predicate
 which will handle the call.
 
 ```
+:- use_module(library(http/http_server)).
+
 text_handler(Request, Response) :-
   http_status_code(Response, 200),
   http_body(Response, text("Welcome to Scryer Prolog!")).
@@ -24,6 +26,7 @@ text_handler(Request, Response) :-
 parameter_handler(User, Request, Response) :-
   http_body(Response, text(User)).
 
+run:-
   http_listen(7890, [
     get(echo, text_handler),                 % GET /echo
     post(user/User, parameter_handler(User)) % POST /user/<User>