"Online recently" feature is unexplained on mobile

[Raton-Laveur]

Steps to reproduce:

1. on a PC browser:

• wonder what's the new green ring icon on the corner of a profile
• mouse over it, see "Online recently'
• go on with your day

2. on mobile app:

• wonder what's the new green ring icon on the corner of a profile
• tap on it, which sends you to user profile
• tap on it again near username, nothing happens
• lose sleep over it

I understand this feature has been added through #808 , but there's no explanation towards user - no FAQ, popup or blog post. Thus, only explaining is done on browser version; mobile users are left unexplained.