diff --git a/rust/README.md b/rust/README.md
index fea9521..f77d0b5 100644
--- a/rust/README.md
+++ b/rust/README.md
@@ -9,3 +9,14 @@ $ docker run --rm -it -v $(pwd):/source schickling/rust
 ```
 
 Mount your local source folder to the container and compile & run code inside.
+
+### Environment variables
+
+#### `USER`
+
+The `$USER` environment variable can be specified, which is used by `cargo`. The default is `root`.
+
+```sh
+$ docker run --rm -it -e USER="John Doe" -v $(pwd):/source schickling/rust
+```
+