reflow the stack size story

Author: tshepang

library/std/src/thread/mod.rs

@@ -124,8 +124,10 @@
 //!
 //! ## Stack size
 //!
-//! The default stack size is platform-dependent and subject to change. Currently it is 2MB on all
-//! Tier-1 platforms. There are two ways to manually specify the stack size for spawned threads:
+//! The default stack size is platform-dependent and subject to change.
+//! Currently, it is 2 MiB on all Tier-1 platforms.
+//!
+//! There are two ways to manually specify the stack size for spawned threads:
 //!
 //! * Build the thread with [`Builder`] and pass the desired stack size to [`Builder::stack_size`].
 //! * Set the `RUST_MIN_STACK` environment variable to an integer representing the desired stack