Add comment for function

Author: tiif

src/shims/unix/fd.rs

@@ -626,6 +626,8 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
         Ok(())
     }
 
+    /// This function write bytes to the user supplied buffer and write the total number of bytes
+    /// written to the dest place. (TODO: fix phrasing later, this function might change)
     fn read_byte_helper(
         &mut self,
         buf: Pointer,