docs: update exec and exec_all parity notes

README.md

@@ -53,10 +53,10 @@ Implemented commands:
 - If `<castle>/.homesickrc` exists and `<castle>/.homesick.d/parity.rb` does not, generates `parity.rb` before execution.
 - Never overwrites an existing `parity.rb` wrapper.
 
-Not yet implemented:
+### exec behavior
 
-- `exec`
-- `exec_all`
+- `exec CASTLE COMMAND...` runs the shell command inside the target castle root.
+- `exec_all COMMAND...` runs the same shell command inside each cloned castle root in sorted order.
 
 ## Outstanding Feature Checklist
 
@@ -68,8 +68,8 @@ Command parity:
 - [x] `destroy`
 - [x] `cd`
 - [x] `open`
-- [ ] `exec`
-- [ ] `exec_all`
+- [x] `exec`
+- [x] `exec_all`
 - [x] `generate`
 
 Historical flag/behavior parity: