add releasing doc

Releasing.md

@@ -0,0 +1,15 @@
+# Creating a Release
+
+- create branch release/1.x.y
+- update debian/changelog
+- create PR, merge when approved
+- on updated master, git tag and push:
+    ```
+    version=$(dpkg-parsechangelog -S Version)
+    git tag -a v$version -m 'aptly: release $version'
+    git push aptly-dev v$version
+    ```
+- run swagger locally
+- add generated swagger-1.x.y.json to www.aptly.info
+- releae www.aptly.info
+- create release announcement on https://github.com/aptly-dev/aptly/discussions