Doc: Fix Qt Help license information

Change-Id: Idbaae38cc24e36f1309995bf7c4f47a41c08db5c
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@qt.io>

src/assistant/help/doc/src/qthelp-index.qdoc

@@ -58,8 +58,9 @@
 
     \section1 License Information
 
-    Qt Core is available under commercial licenses from \l{The Qt Company}.
-    In addition, it is available under the
+    Qt Help is available under commercial licenses from \l{The Qt Company}.
+    In addition, it is available under free software licenses. Since Qt 5.4,
+    these free software licenses are
     \l{GNU Lesser General Public License, version 3}, or
     the \l{GNU General Public License, version 2}.
     See \l{Qt Licensing} for further details.