Add docs for sys/random.h

src/header/sys_random/mod.rs

@@ -1,3 +1,7 @@
+//! `sys/random.h` implementation.
+//!
+//! Non-POSIX, see <https://www.man7.org/linux/man-pages/man2/getrandom.2.html>.
+
 use core::slice;
 
 use crate::{
@@ -5,9 +9,12 @@ use crate::{
     platform::{types::*, Pal, Sys},
 };
 
+/// See <https://www.man7.org/linux/man-pages/man2/getrandom.2.html>.
 pub const GRND_NONBLOCK: c_uint = 1;
+/// See <https://www.man7.org/linux/man-pages/man2/getrandom.2.html>.
 pub const GRND_RANDOM: c_uint = 2;
 
+/// See <https://www.man7.org/linux/man-pages/man2/getrandom.2.html>.
 #[no_mangle]
 pub unsafe extern "C" fn getrandom(buf: *mut c_void, buflen: size_t, flags: c_uint) -> ssize_t {
     Sys::getrandom(