fix: improves panic messages when there is no reactor/timer

tokio/src/io/driver/mod.rs

@@ -198,7 +198,9 @@ impl Handle {
     ///
     /// This function panics if there is no current reactor set.
     pub(super) fn current() -> Self {
-        context::io_handle().expect("no current reactor")
+        context::io_handle().expect(
+            "there is no reactor running, this code must be executed from within a tokio runtime",
+        )
     }
 
     /// Forces a reactor blocked in a call to `turn` to wakeup, or otherwise

tokio/src/time/error.rs

@@ -64,7 +64,9 @@ impl fmt::Display for Error {
     fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
         use self::Kind::*;
         let descr = match self.0 {
-            Shutdown => "timer is shutdown",
+            Shutdown => {
+                "the timer is shutdown, this code must be executed from within a tokio runtime"
+            }
             AtCapacity => "timer is at capacity and cannot create a new entry",
         };
         write!(fmt, "{}", descr)