message: docs: add temporary note on .deb section about x86
  Clarify that (at least for now) the built .deb file is for x86. See
diff: @@ -126,7 +126,7 @@ There is an official package that can be installed with `pacman`:
  sudo pacman -Syu bottom
  ```
  -### Debian/Ubuntu
  +### Debian/Ubuntu (x86-64)
  A `.deb` file is provided on each [release](https://github.com/ClementTsang/bottom/releases/latest):
  