Add notes on using with act to the README

README.md

@@ -75,6 +75,15 @@ So, we recommend [defining] `GITHUB_TOKEN`, as seen in the [example workflow], w
 [defining]: https://docs.github.com/en/actions/learn-github-actions/variables
 [example workflow]: #example-workflow
 
+## Use with [act]
+
+[act] is a tool which can be used to run GitHub workflows locally, using Docker. It is possible to use the `xtensa-toolchain` action with [act]; however, due to the fact that [espup] queries the GitHub API, it is necessary to set the `GITHUB_TOKEN` environment variable in order to do so.
+
+For more information please see the [`GITHUB_TOKEN`] section of the `README` for [act].
+
+[act]: https://github.com/nektos/act
+[`GITHUB_TOKEN`]: https://github.com/nektos/act#github_token
+
 ## License
 
 Licensed under either of: