Auto merge of rust-lang#41122 - palango:mod-desc-floats, r=frewsxcv

Improve module description for std::f32 and std::f64

Fixes rust-lang#29353, see discussion there.

Author: bors

src/libstd/f32.rs

@@ -8,7 +8,9 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-//! The 32-bit floating point type.
+//! This module provides constants which are specific to the implementation
+//! of the `f32` floating point data type. Mathematically significant
+//! numbers are provided in the `consts` sub-module.
 //!
 //! *[See also the `f32` primitive type](../primitive.f32.html).*
 

src/libstd/f64.rs

@@ -8,7 +8,9 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-//! The 64-bit floating point type.
+//! This module provides constants which are specific to the implementation
+//! of the `f64` floating point data type. Mathematically significant
+//! numbers are provided in the `consts` sub-module.
 //!
 //! *[See also the `f64` primitive type](../primitive.f64.html).*