Document effect of setting quantity to 0 in README

[JonasScharpf]

This relates to already solved #198

Testing done

N/A only documentation

Proposed upgrade guidelines

N/A

Localizations

N/A

Submitter checklist

• The Jira / Github issue, if it exists, is well-described.
  • The changelog generator for plugins uses the pull request title as the changelog entry.
  • Fill in the Proposed upgrade guidelines section only if there are breaking changes or changes that may require extra steps from users during the upgrade.
• There is automated testing or an explanation that explains why this change has no tests.
• Changes in the interface are documented also as examples.

Maintainer checklist

Before the changes are marked as ready-for-merge:

• There is at least one (1) approval for the pull request and no outstanding requests for change.
• Conversations in the pull request are over, or it is explicit that a reviewer is not blocking the change.
• Changelog entries in the pull request title and/or Proposed changelog entries are accurate, human-readable, and in the imperative mood.
• Proper changelog labels are set so that the changelog can be generated automatically. See also release-drafter-labels.
• If the change needs additional upgrade steps from users, the upgrade-guide-needed label is set and there is a Proposed upgrade guidelines section in the pull request title (see example).
• java code changes are tested by automated test.

[mPokornyETM]

LGTM

[mPokornyETM]

@JonasScharpf thx and welcome in the community