add #![deny(missing_docs)] AND #![deny(warnings)] in main.rs, and add more comments

os/src/task/task.rs

@@ -1,9 +1,12 @@
+//! Types related to task management
+
 use super::TaskContext;
 
 #[derive(Copy, Clone)]
 pub struct TaskControlBlock {
     pub task_status: TaskStatus,
     pub task_cx: TaskContext,
+    // LAB1: Add whatever you need about the Task.
 }
 
 #[derive(Copy, Clone, PartialEq)]