Work around localhost link problem with <link> syntax

[http://localhost]() syntax used previously doesn't actually work. Link
is created, but link is back to self.

Per a [hot tip][1], now using <http://localhost> syntax, which works
perfectly.

[1]: https://github.com/vmg/sundown/issues/132#issuecomment-8774103

README.md

 Test the service
 ----------------
 
-Once the service starts, you can test it by pointing your web browser at [http://localhost:8080/hello-world](). Or you can consume it from the command line using [`curl`][curl]:
+Once the service starts, you can test it by pointing your web browser at <http://localhost:8080/hello-world>. Or you can consume it from the command line using [`curl`][curl]:
 
 ```
 $ curl http://localhost:8080/hello-world
 {"id":1,"content":"Hello, World!"}
 ```
 
-Now try providing a `name` query string parameter: [http://localhost:8080/hello-world?name=User]()
+Now try providing a `name` query string parameter: <http://localhost:8080/hello-world?name=User>
 
 ```
 $ curl http://localhost:8080/hello-world?name=User