add deadline Wikipedia link

Author: vladak

docs/index.html

@@ -168,7 +168,8 @@ <h2><a name="final_assignment">Final Lab Assignment</a></h2>
 22, 2023, CET</b>.  You need to send the e-mail before the deadline.  The date
 stands even if the semester is prolonged.
 
-<p>The deadlines are hard requirements so stick to the schedule.  We do not
+<p>The deadlines are <a href="https://en.wikipedia.org/wiki/Time_limit">hard
+requirements</a> so stick to the schedule.  We do not
 accept late arrivals and that automatically means you are not eligible for the
 credits for the year.  Obviously, you can send us the whole thing in one step
 before the first deadline, no need to separate the project in two parts.