tor-browser-bundle-bin: add comment explaining allowSubstitutes=false

[ghost]

Closed by #192220

Description of changes

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandbox = true set in nix.conf? (See Nix manual)
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 22.11 Release Notes (or backporting 22.05 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
  • (Release notes changes) Ran nixos/doc/manual/md-to-db.sh to update generated release notes
• Fits CONTRIBUTING.md.

The comments added by this commit are my summary of @joachifm's (very patient)
explanation of the reason for hydraPlatforms=[] (bandwidth) and
allowSubstitutes=false; (don't bother checking because it isn't on
cache.nixos.org anyways).

[ghost]

More details here: https://discourse.nixos.org/t/why-is-caching-for-tor-browser-bundle-bin-disabled/16499/2

and in the commit message for ecd0e1a

I'll revisit this in the morning and either add more information or close it.

[SuperSandro2000]

The source is only a small 108M and the final build 251M which should not make any difference for hydra or the CDN. Also this is a recuring problem, so I firmly believe we try to save bandwidth at the wrong point here. Closing and removing that from meta in my PR.