prepare for 5.0.1 [ci skip]

Author: KrisThielemans

VERSION.txt

@@ -1 +1 @@
-5.0.0
+5.0.1

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_5.0.htm">version 5.0.1 (dated 11 May 2022)</a></li>
 <li><a href="release_5.0.htm">version 5.0.0 (dated 22 March 2022)</a></li>
 <li><a href="release_4.1.htm">version 4.1.0 (dated 02 May 2021)</a></li>
 <li><a href="release_4.0.htm">version 4.0.2 (dated 22 May 2020)</a></li>