fix documentation

Author: Qelxiros

library/std/src/os/unix/process.rs

@@ -385,7 +385,8 @@ pub trait ChildExt: Sealed {
     /// # Errors
     ///
     /// This function will return an error if the signal is invalid. The integer values associated
-    /// with signals are implemenation-specific, so the use of [`libc`] is encouraged.
+    /// with signals are implemenation-specific, so it's encouraged to use a crate that provides
+    /// posix bindings.
     ///
     /// # Examples
     ///