Create documentation how to find story from Backlog #2276

Task summary

Our internal contributing documentation has improved a lot lately but still it is not clearly documented how to select a new story from the backlog.
We have

• https://github.com/devonfw/IDEasy/blob/main/documentation/contributing/issue.adoc
• https://github.com/devonfw/IDEasy/blob/main/documentation/contributing/project-board.adoc#example-project-board

However, both pages are slightly related but do not really answer the question "how do I find a new story from the backlog?".

IMHO the issue.adoc would be the intuitive place to add this information:

• Add a new section titled Backlog
• Add a description how to choose a new issue explaining ready-to-implement label, priority, good-first-issue label, etc.
• Provide issue query link: https://github.com/devonfw/IDEasy/issues?q=is%3Aissue%20state%3Aopen%20no%3Aassignee%20label%3Aready-to-implement
• Also link to the project board example (see link above)
• Explicitly remind that the first thing to do is to self-assign yourself to the issue before you start working.

Additional context

No response