doc: add documents of some crates

Author: equation314

src/lib.rs

@@ -1,5 +1,12 @@
 //! `no_std` spin lock implementation that can disable kernel local IRQs or
 //! preemption while locking.
+//!
+//! # Cargo Features
+//!
+//! - `smp`: Use in the **multi-core** environment. For **single-core**
+//!   environment (without this feature), the lock state is unnecessary and
+//!   optimized out. CPU can always get the lock if we follow the proper guard
+//!   in use. By default, this feature is disabled.
 
 #![cfg_attr(not(test), no_std)]
 #![feature(const_trait_impl)]
@@ -10,7 +17,7 @@ use kernel_guard::{NoOp, NoPreempt, NoPreemptIrqSave};
 
 pub use self::base::{BaseSpinLock, BaseSpinLockGuard};
 
-/// A spin lock that disbales kernel preemption while trying to lock, and
+/// A spin lock that disables kernel preemption while trying to lock, and
 /// re-enables it after unlocking.
 ///
 /// It must be used in the local IRQ-disabled context, or never be used in