Add f32 and f64 examples warning

Author: GuillaumeGomez

src/libstd/primitive_docs.rs

@@ -488,6 +488,9 @@ mod prim_tuple { }
 ///
 /// *[See also the `std::f32` module](f32/index.html).*
 ///
+/// However, please note that examples are shared between the `f64` and `f32`
+/// primitive types. So it's normal if you see usage of `f64` in there.
+///
 mod prim_f32 { }
 
 #[doc(primitive = "f64")]
@@ -496,6 +499,9 @@ mod prim_f32 { }
 ///
 /// *[See also the `std::f64` module](f64/index.html).*
 ///
+/// However, please note that examples are shared between the `f64` and `f32`
+/// primitive types. So it's normal if you see usage of `f32` in there.
+///
 mod prim_f64 { }
 
 #[doc(primitive = "i8")]