docs: say which OS each Packaging command belongs to

The two package-* invocations sat next to each other with nothing but
the code-fence language to tell them apart, and the output paths were
pooled in one block that mixed Linux tarballs with the Windows zip.
Label each command Windows: / Linux: like Run From Source does, and give
each its own artifact list.

Also note that package-linux.sh emits the arm64 tarball only when
aarch64-linux-gnu-gcc is installed; the flat list implied a plain Linux
host always produces both.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

docs/DEVELOPMENT.md

@@ -225,10 +225,18 @@ dist/windows/gosentry-<version>-windows-amd64.exe
 The `package-*` scripts build the binary for their platform and wrap it in a
 distributable archive together with `README.md` and `CHANGELOG.md`:
 
+Windows:
+
 ```powershell
 scripts\package-windows.bat
 ```
 
+```text
+dist\windows\gosentry-<version>-windows-amd64.zip
+```
+
+Linux:
+
 ```bash
 ./scripts/package-linux.sh
 ```
@@ -236,9 +244,11 @@ scripts\package-windows.bat
 ```text
 dist/linux/gosentry-<version>-linux-amd64.tar.gz
 dist/linux/gosentry-<version>-linux-arm64.tar.gz
-dist\windows\gosentry-<version>-windows-amd64.zip
 ```
 
+The arm64 archive is produced only when the `aarch64-linux-gnu-gcc` cross
+compiler is available; otherwise that target is skipped with a message.
+
 The version stamped into the file names and into the binary comes from
 `src/app/version.go`.