releasing.md

Currently releases of Socomo are done by Wojciech Gdela. Here's the checklist for a release:

1. ./mvnw versions:set -DgenerateBackupPoms=false -DnewVersion=2.X.0
2. ./mvnw clean verify -P release
3. ./dogfood.sh
4. ./catfood.sh
5. commit changes and push to github
6. publish a new release on github with tag v2.X.0
7. attach socomo-standalone-2.x.0.jar to the github release
8. check in browser the socomo.html from socomo-core module
9. ./mvnw clean deploy -P release
10. close staging repository on sonatype manager
11. click the release button
12. after ten minutes check central repository
13. ./mvnw versions:set -DgenerateBackupPoms=false -DnewVersion=2.Y-SNAPSHOT
14. ./dogfood.sh
15. commit changes and push to github