Clarify that the total_time is in seconds

It wasn't clear to me that the time was in seconds and not ms.

```ruby
start_time = Time.now.utc.to_f
# ... 
total_time = (Time.now.utc.to_f - start_time).round(6) 
```

lib/job-iteration/iteration.rb

@@ -14,7 +14,7 @@ module Iteration
     # The time when the job starts running. If the job is interrupted and runs again, the value is updated.
     attr_accessor :start_time
 
-    # The total time the job has been running, including multiple iterations.
+    # The total time (in seconds) the job has been running, including multiple iterations.
     # The time isn't reset if the job is interrupted.
     attr_accessor :total_time