Draft: Add warning/disclaimer message

The goal here is to allow the user to make some sort an informed decision by stating all of the facts without scaring them away, unless if we have a reason to. I am seeking for an initial set of feedback regarding the tone, the language and the threat model-related concerns that I am trying to name here. As always, I am acting based on a set of presumptions:

• A person who uses this download method does not have another way to do so.
• Telegram's protocol hasn't been cracked wide open (allowing for the surveillance of all messages exchanged for the platform).
• DPI could be in use.
• The way Telegram is operated is beyond our control and that we should show some reservations.
• If the said user is targeted by every single already has an infected device, then, uh, tough luck.
• Undetectable obfuscation techniques today may be detectable tomorrow.

Additional remarks:

• The text currently ignores the prospect that the user may already be using a traditional VPN service to access Telegram.

This commit has not been tested on a live instance and some things (such as adding the new strings to the .po file) will be done later. I believe that this step is slightly sensitive, requires transparency and needs opinions from people that have more experience in this than I do.

TL;DR I need feedback.