Improve documentation of Stack size

Author: HintringerFabian

library/std/src/thread/mod.rs

@@ -124,9 +124,8 @@
 //!
 //! ## Stack size
 //!
-//! The default stack size for spawned threads is 2 MiB, though this particular stack size is
-//! subject to change in the future. 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 2MB 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