Fix docs for Command type
diff --git a/README.md b/README.md
index 27e8b9ecf..c986e0527 100644
--- a/README.md
+++ b/README.md
@@ -298,7 +298,7 @@ side_effect(old_command: Command, fixed_command: str) -> None
 ```
 and optional `enabled_by_default`, `requires_output` and `priority` variables.
 
-`Command` has three attributes: `script`, `stdout`, `stderr` and `script_parts`.
+`Command` has four attributes: `script`, `stdout`, `stderr` and `script_parts`.
 Rule shouldn't change `Command`.
 
 

![1 8](https://user-images.githubusercontent.com/116432/29601317-d1e93364-87d2-11e7-8c14-c8af5ca3273b.jpg)
