Feature/yq on windows (#336)

* install `yq` if runner.os is `windows`

* update readme with `yq` on windows info

README.md

@@ -60,10 +60,12 @@ steps:
 >   flutter: ">= 3.19.0 <4.0.0"
 > ```
 
-> [!WARNING]
+> [!NOTE]
 >
 > Using `flutter-version-file` requires [`yq`](https://github.com/mikefarah/yq),
-> which is not pre-installed in `windows` images. Install it yourself.
+> which is not pre-installed in `windows` runners. Fortunately, since version
+> 2.18.0, this action installs `yq` automatically, so no action is required from
+> you.
 
 ### Use latest release for particular channel