Adding time tracking to feature list (#2982)

Now that 1.3 is out time tracking is a new feature
go-gitea/docs#148

Author: techknowlogick

docs/content/page/index.en-us.md

@@ -181,6 +181,7 @@ The goal of this project is to make the easiest, fastest, and most painless way
         - Milestones
         - Labels
         - Assign issues
+        - Track time
         - Filter
             - Open
             - Closed