Document the Linux -> Windows NSIS cross-compile setup

Adds notes for hosts without an nsis package: sourcing makensis, pointing
it at a full NSIS 3.11 data directory, and pre-seeding Tauri's NSIS plugin cache.

Co-authored-by: CommandCodeBot <noreply@commandcode.ai>

README.md

@@ -70,6 +70,26 @@ npm run app:build:windows
 Output lands in `src-tauri/target/x86_64-pc-windows-msvc/release/bundle/nsis/` and the
 portable binary in the sibling `release/` folder.
 
+### Notes for Linux hosts without an `nsis` package
+
+`makensis` is required for the installer, and Tauri also fetches a small NSIS plugin. On
+distributions that don't package NSIS (e.g. Void Linux):
+
+1. Provide `makensis` (e.g. extract it from your distribution's or an upstream package) and
+   put it on `PATH`.
+2. Point `makensis` at a full NSIS data directory (3.11 recommended, for `Win/RestartManager.nsh`);
+   it looks in the directory compiled into the binary unless `NSISDIR` is set.
+3. Pre-seed Tauri's plugin cache so it does not have to download it:
+
+   ```
+   mkdir -p ~/.cache/tauri/NSIS/Plugins/x86-unicode/additional
+   # nsis_tauri_utils.dll (SHA1 75197fee3c6a814fe035788d1c34ead39349b860)
+   #   from https://github.com/tauri-apps/nsis-tauri-utils/releases
+   ```
+
+With those in place, `npm run app:build:windows` produces the NSIS `-setup.exe` and the
+portable `voiced.exe`.
+
 ## Where data lives
 
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