Added PSR-2 documentation XML files

[blue32a]

Thank you for providing a great tool.

Description

I was looking into sniffs to create a coding standard for my project and it took me a long time to get to the generator. I found some missing in the documentation and am submitting this PR. Hope that helps.

Suggested changelog entry

• Added missing PSR-2 documentation XML files.

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)
• [ ] This change is only breaking for integrators, not for external standards or end-users.
• [x] Documentation improvement

PR checklist

• [x] I have checked there is no other PR open for the same change.
• [x] I have read the Contribution Guidelines.
• [x] I grant the project the right to include and distribute the code under the BSD-3-Clause license (and I have the right to grant these rights).
• [ ] I have added tests to cover my changes.
• [ ] I have verified that the code complies with the projects coding standards.
• [ ] [Required for new sniffs] I have added XML documentation for the sniff.
• [x] [Required for new files] I have added any new files to the package.xml file.

[jrfnl]

P.S.: The new files should also be added to the package.xml file.

[blue32a]

@jrfnl Thank you for your review.

I have updated the PR with your findings.

[blue32a]

I had missed it. Three new documents have been added to package.xml.

[jrfnl]

FYI: this fix is included in today's PHP_CodeSniffer 3.8.0 release.

As per #3932, development on PHP_CodeSniffer will continue in the PHPCSStandards/PHP_CodeSniffer repository. If you want to stay informed, you may want to start "watching" that repo (or watching releases from that repo).