README: the versions it names are the versions that exist

Every README here opens by showing what a program writes in its manifest, which
is the first thing a reader copies and the last thing anyone edits. These lines
had drifted --- the specification's own README asked for a version four minor
releases old --- and nothing checked them.

`openkal/tools/check-readme-versions.sh` now does.

Author: speak-agent

README.md

@@ -4,10 +4,10 @@ An implementation of [openkal](https://github.com/mcpplibs/openkal) for Windows.
 
 ```toml
 [dependencies]
-openkal = "0.8.0"
+openkal = "0.9.0"
 
 [target.'cfg(windows)'.dependencies]
-openkal-windows = "0.3.0"
+openkal-windows = "0.4.0"
 ```
 
 Its purpose is as much to test the specification as to be used. openkal was