Updated "SimpleX Chat Privacy Policy and Conditions of Use"

The updated document: https://github.com/simplex-chat/simplex-chat/blob/stable/PRIVACY.md

The changes: https://github.com/simplex-chat/simplex-chat/pull/3796/files

TL;DR:
- it clarifies that we develop software for communication network, and not a communication service.
- it highlights the requirement of AGPLv3 license to publish any code modifications, and our commitment to run unmodified code.

Let us know any comments / questions!