translate “工作 996，生病 ICU” to english version. (#992)

Thanks for your discussion and contribution.

en_US.md

@@ -2,6 +2,9 @@
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 ## What is "996"?
+
+996 working, ICU waiting.
+
 A "996" work schedule refers to an unofficial work schedule (9 am - 9 pm, 6 days a week) that has been gaining more popularity. 
 Serving a company that encourages the "996" work schedule usually means work for at least 60 hours a week.