Add a note about path expansion on Windows.

README.md

@@ -248,6 +248,9 @@ A cache today is immutable and cannot be updated. But some use cases require the
 #### Use cache across feature branches
 Reusing cache across feature branches is not allowed today to provide cache [isolation](https://docs.github.com/en/actions/using-workflows/caching-dependencies-to-speed-up-workflows#restrictions-for-accessing-a-cache). However if both feature branches are from the default branch, a good way to achieve this is to ensure that the default branch has a cache. This cache will then be consumable by both feature branches.
 
+#### Windows environment variables
+Please note that Windows environment variables (like `%LocalAppData%`) will NOT be expanded by this action. Instead, prefer using `~` in your paths which will expand to HOME directory. For example, instead of `%LocalAppData%`, use `~\AppData\Local`. For a list of supported default environment variables, see [this](https://docs.github.com/en/actions/learn-github-actions/environment-variables) page. 
+
 ## Contributing
 We would love for you to contribute to `actions/cache`, pull requests are welcome! Please see the [CONTRIBUTING.md](CONTRIBUTING.md) for more information.