Add sha256sums and gpg sign outside of maven process

Signed-off-by: Andrew DeMaria <lostonamountain@gmail.com>

contrib/release.md

@@ -20,37 +20,41 @@ Release Steps
 
 6. Package
 
-        mvn clean verify -P docker,sign
+        mvn clean verify -P docker
 
-7. push up branch and tag
+7. Sign sha256sums file
+
+        gpg2 --clearsign artifacts-checksums.sha
+
+8. push up branch and tag
 
         git push origin vX.Y.Z
         git push -u origin release-X.Y
 
-8. Create new release on github
+9. Create new release on github
 
    - Draft new Relase
    - Choose existing tag
    - Title is "Airsonic X.Y.Z"
    - Contents are the relevant entry of the CHANGELOG.md file
-   - Upload `airsonic.war` and `airsonic.war.asc`
+   - Upload `airsonic.war` and `artifacts-checksums.sha`
 
-9. Update latest docker tag
+10. Update latest docker tag
 
         docker tag airsonic/airsonic:X.Y.Z-RELEASE airsonic/airsonic:latest
 
-10. Docker login with airsonic credentials in `airsonic-passwords` repo
+11. Docker login with airsonic credentials in `airsonic-passwords` repo
 
         docker login
 
-11. Push images
+12. Push images
 
         docker push airsonic/airsonic:X.Y.Z-RELEASE
         docker push airsonic/airsonic:latest
 
-12. Checkout master branch and bump maven version to next snapshot version
+13. Checkout master branch and bump maven version to next snapshot version
 
         git checkout master
         mvn versions:set -DnewVersion=X.Y+1.0-SNAPSHOT
 
-13. Git commit and push
+14. Git commit and push