Update readme.txt

Add progressplanner as a contributor

Author: jdevalk

readme.txt

@@ -1,5 +1,5 @@
 === Comment-free zone ===
-Contributors: joostdevalk, aristath, mariekerakt, irisguelen, samalderson
+Contributors: progressplanner, joostdevalk, aristath, mariekerakt, irisguelen, samalderson
 Tags: planning, maintenance, writing, blogging
 Requires at least: 6.3
 Tested up to: 6.7
@@ -52,4 +52,4 @@ If you've found a bug, please follow the following steps:
 
 = 1.0 =
 
-* Initial release.
+* Initial release.