diff --git a/README.md b/README.md
index c7b87db..a653acb 100644
--- a/README.md
+++ b/README.md
@@ -38,3 +38,9 @@ If you want to use this in your own infrastructure, setup your AWS credentials w
 ```
 
 Be aware of S3 transfer costs if your runners are not in the same AWS region as your bucket.
+
+## Special environment variables
+
+* `RUNS_ON_S3_BUCKET_CACHE`: if set, the action will use this bucket to store the cache.
+* `RUNS_ON_S3_FORCE_PATH_STYLE` or `AWS_S3_FORCE_PATH_STYLE`: if one of those environment variables equals the string `"true"`, then the S3 client will be configured to force the path style.
+