docs: mark cd parity complete

README.md

@@ -39,6 +39,7 @@ Implemented commands:
 - `push [CASTLE]`
 - `commit -m MESSAGE [CASTLE]`
 - `destroy [CASTLE]`
+- `cd [CASTLE]`
 - `rc [CASTLE]`
 - `version`
 
@@ -52,7 +53,6 @@ Implemented commands:
 
 Not yet implemented:
 
-- `cd`
 - `open`
 - `exec`
 - `exec_all`
@@ -66,7 +66,7 @@ Command parity:
 - [x] `push`
 - [x] `commit`
 - [x] `destroy`
-- [ ] `cd`
+- [x] `cd`
 - [ ] `open`
 - [ ] `exec`
 - [ ] `exec_all`