diff --git a/README.md b/README.md
index 065a0563..34ebe565 100644
--- a/README.md
+++ b/README.md
@@ -13,3 +13,7 @@ Add this to your `Cargo.toml`:
 [dependencies]
 getopts = "0.2"
 ```
+
+## Contributing
+
+The `getopts` library is used by `rustc`, so we have to be careful about not changing its behavior.