Add missing comment for f64

Author: bmoxb

library/core/src/convert/num.rs

@@ -182,7 +182,8 @@ impl const From<bool> for f32 {
 #[stable(feature = "float_from_bool", since = "1.68.0")]
 #[rustc_const_unstable(feature = "const_num_from_num", issue = "87852")]
 impl const From<bool> for f64 {
-    /// Converts `bool` to `f64` losslessly.
+    /// Converts `bool` to `f64` losslessly. The resulting value is positive
+    /// `0.0` for `false` and `1.0` for `true` values.
     #[inline]
     fn from(small: bool) -> Self {
         small as u8 as Self