diff --git a/README.md b/README.md
index 492913b..e46b89e 100644
--- a/README.md
+++ b/README.md
@@ -12,6 +12,7 @@ I want to learn Rust and see how much effort I can put into making an interopera
 - [ ] Environment variables
 - [ ] Builtins
   - [x] `cd`
+  - [x] `:`
   - [ ] `set`
   - [ ] `alias`
   - [ ] `type`