Update documentation per Release

Created by: andygrunwald

Idea

Quote by @M4LuZ from https://github.com/lansuite/lansuite/pull/202#discussion_r181548838

A general update documentation(per release) is a good idea, also started one in the wiki a while ago: https://github.com/lansuite/lansuite/wiki/HowTo%3A-Upgrade-from-Release-4.2 I would only document the queries that cannot be covered by the existing db update (e.g. necessary DML statements or preparative / rollback steps), because the rest can be seen either by a diff of the XML documents or by just looking at the generated DDL statements on execution

Possible Solution

Create a markdown file like the symfony/symfony project. Example: symfony/symfony: UPGRADE-5.0.md

Why markdown and not the Wiki? With this a code review can take place to ensure a) quality and b) understanding of multiple persons instead of one. Because often the one who wrote, is way to deep into the problem to describe the upgrade to people who are not aware of the details of the issue.