Feature request: better explanation for disappearing messages

[crtlib]

• I have searched open and closed issues for duplicates

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When enabling disappearing messages in, for example, Android client, you're presented with a valuable hint "Messages sent and received in this conversation will disappear %s after they have been seen". To avoid confusion something similar is needed in Desktop client as well.

Would like to implement this, so please guide whether there should be a new dialog or just an additional label somewhere is also OK.

[scottnonnenberg-signal]

I think a popup the moment you turn on disappearing messages for the first time might be appropriate. It would need a global setting to ensure that you aren't bothered with it every time.

It's worth mentioning that the vast majority of users experience disappearing messages first in their mobile app of choice. So, while this is good for usability, it's focused on a relatively small group of users.