Fix markdown syntax in README.packaging.md

debian/README.packaging.md

@@ -12,6 +12,7 @@ gbp buildpackage
 
 ## Build a release
 
+```
 export VERSION=4.1.0
 git fetch --all
 gbp import-ref --merge-mode=replace -u ${VERSION?}
@@ -22,3 +23,4 @@ quilt push -a --refresh ; quilt pop -a ; rm .pc/ -rf
 dch --release --distribution stable ""
 git commit -m "Release ${VERSION?}-1" debian/changelog
 gbp buildpackage
+```