update history.htm [ci skip]

Author: KrisThielemans

documentation/history.htm

@@ -11,6 +11,7 @@ <h1>History of public releases of the STIR software</h1>
 The following links give you a summary what has changed. However,
 the ChangeLog is the definite (but tedious) information.
 <ul >
+<li><a href="release_6.0.htm">version 6.0.0 (dated 07 February 2024)</a></li>
 <li><a href="release_5.2.htm">version 5.2.0 (dated 30 October 2023)</a></li>
 <li><a href="release_5.1.htm">version 5.1.2 (dated 10 September 2023)</a></li>
 <li><a href="release_5.1.htm">version 5.1.1 (dated 26 Augustus 2023)</a></li>
@@ -48,7 +49,7 @@ <h1>History of public releases of the PARAPET software</h1>
 
 <!-- Created: Wed Jul 19 16:03:02 BST 2000 -->
 <!-- hhmts start -->
-Last modified: 29 October 2023
+Last modified: 7 February 2024
 <!-- hhmts end -->
   </body>
 </html>