add doc desc

src/data_time.rs

@@ -52,6 +52,9 @@ impl DateTime {
 
     #[cfg(not(feature = "tzdb"))]
     pub fn local_now() -> Result<Self, Box<dyn Error>> {
+        // Warning: Attempt to create a new OffsetDateTime with the current date and time in the local offset. If the offset cannot be determined, an error is returned.
+        // At present, using it on MacOS return error. Use it with careful.
+        // Suggestion use feature tzdb crate exposed function at below.
         OffsetDateTime::now_local()
             .map(DateTime::Local)
             .map_err(|e| e.into())