* Change URL from Open Whisper Systems site to Signal's site (the former always redirects to the latter anyways)
* Delete mention of checking if two words match during 1-on-1 Signal calls in block quote (I haven't seen this on Signal mobile since at least October 2020, when group calls came to desktop & iPad)
* Update info on Signal being developed/supported by Signal Foundation and Signal Messenger LLC, which have superseded Open Whisper Systems after 2018
* Add distinction of FOSS license between mobile clients and desktop client+server
* State clearly that Signal Desktop will be installed on Qubes OS
* Add reference to official Linux instructions from Signal
* Move clarifying notes in Step 3 commands to Bash comments at end of file, to better simulate terminal emulator standard output
* Make typographical style more consistent throughout the list
