doc: document PCSCLite::close, CardReader::close

- Update example accordingly.

examples/example.js

@@ -37,6 +37,8 @@ pcsc.on('reader', function(reader) {
                                 console.log(err);
                             } else {
                                 console.log('Data received', data);
+                                reader.close();
+                                pcsc.close();
                             }
                         });
                     }