Merge #752: Modify command line help to show support for BIP21 URIs

ede5014 Modify command line help to show support for BIP21 URIs (Hernan Marino)

Pull request description:

  While reviewing a different PR (see #742 ) **hebasto** suggested that the help for bitcoin-qt should be updated to reflect the fact that bitcoin-qt supports an optional BIP21 URI parameter.

  Since this reflects actual behaviour of bitcoin-qt and is independent of whether or not the other PR gets merged, I created this simple PR to fix the help message.

ACKs for top commit:
  kristapsk:
    utACK ede5014
  pablomartin4btc:
    lgtm, re ACK ede5014
  hebasto:
    ACK ede5014.

Tree-SHA512: c456297c486bc5cc65e0e092e7ba9d51b0bd7a584d4fabca7f7ca1f8e58cbcc66e96226539c689ed0f5e7f40da220bbc4ea30b90e31e1aeeb8867a385a90209c

src/qt/utilitydialog.cpp

@@ -58,7 +58,8 @@ HelpMessageDialog::HelpMessageDialog(QWidget *parent, bool about) :
         ui->helpMessage->setVisible(false);
     } else {
         setWindowTitle(tr("Command-line options"));
-        QString header = "Usage:  bitcoin-qt [command-line options]                     \n";
+        QString header = "Usage: bitcoin-qt [command-line options] [URI]\n\n"
+                         "Optional URI is a Bitcoin address in BIP21 URI format.\n";
         QTextCursor cursor(ui->helpMessage->document());
         cursor.insertText(version);
         cursor.insertBlock();