Document new zip ball generation

.gitignore

@@ -1,12 +1 @@
-bootstrap
-bootstrap-aarch64.zip
-bootstrap-i686.zip
-bootstrap-x86_64.zip
-nix-*-aarch64-linux.tar.bz2
-nix-*-i686-linux.tar.bz2
-nix-*-x86_64-linux.tar.bz2
-proot-host
-proot-aarch64
-proot-i686
-proot-x86_64
-qemu-aarch64
+result

README.md

@@ -31,12 +31,14 @@ The [terminal emulator part](https://github.com/t184256/nix-on-droid-app)
 is probably not interesting for you, just download and use a prebuilt one.
 If you really want to rebuild it, you can just use Android Studio for that.
 
-The zipball generation script is probably what you are after.
-Get an x86_64 computer with Nix
-(running a reasonably recent version of NixOS would work out the best).
-Modify the script, run it as `./generate_bootstrap_zipball aarch64`
-or `./generate_bootstrap_zipball i686`,
-put the resulting files on some HTTP server,
+The zipball generation is probably what you are after.
+Get an x86_64 computer with Nix. Run one of the following:
+```
+nix build -f ./src --argstr arch aarch64 bootstrapZip
+nix build -f ./src --argstr arch i686 bootstrapZip
+```
+
+Put the zip file found `result` on some HTTP server
 and specify the parent directory URL during the installation.
 To re-trigger the installation, use
 'clear data' on the Android app (after backing stuff up, obviously).
@@ -68,4 +70,3 @@ but has no relation to Termux-the-distro.
 
 Previous project that did use Termux-the-distro:
 https://github.com/t184256/nix-in-termux
-