Create nihal_arch_packaging.md

Author: ashitaprasad

doc/proposals/2025/fosshack/nihal_arch_packaging.md

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+# Add Arch Linux packaging instructions and CI Pipeline
+
+Issue - https://github.com/foss42/apidash/issues/545  
+PR - https://github.com/foss42/apidash/pull/594  
+Link - https://fossunited.org/hack/fosshack25/p/e5n4kirnno
+
+A GitHub action is triggered on new version tags when `pubspec.yaml` changes
+
+It:
+  - Extracts version from pubspec.yaml
+  - Downloads and generates checksums for the .deb package and LICENSE
+  - Updates the PKGBUILD with new version and checksums
+  - Publishes to AUR using the KSXGitHub/github-actions-deploy-aur action
+
+The following secrets need to be added to the GitHub repository:
+
+- `AUR_USERNAME`: Maintainer's AUR username
+- `AUR_EMAIL`: Maintainer's AUR email address
+- `AUR_SSH_PRIVATE_KEY`: Maintiner's SSH private key with AUR access
+
+Adding workflow for `.deb` turned out to be complex than I had thought.  
+I have added the support for arm64 and this will assume `.deb` files are available at release time.  
+If they’re not, it will fail, prompting manual intervention or a separate release process.