Update README.md

README.md

@@ -9,7 +9,7 @@ An awesome list of open source statistical software packages useful for creating
 2. it is confirmed to be used in the production of official statistics by at least one institute, or
 3. it provides access to official statistics publications.
 
-We prefer packages that are reasonably easy to install and use and that
+We prefer packages that are reasonably easy to install and use, that have at least one stable version, and that
 are actively maintained.
 
 [Contributions](#contributions) are welcome.