Update README.md to reference latest version

[Tylopilus]

Description

With the release of 53 the readme was update to use archetype-plugin:3.3.1

this change only works if the archetype-post-generate.groovy script also references groovy.xml.XmlSlurper instead of groovy.util.XmlSlurper

Related Issue

#1274
#1276

Motivation and Context

making it work

How Has This Been Tested?

locally executing with proper version of archetype

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)

Checklist:

• I have signed the Adobe Open Source CLA.
• My code follows the code style of this project.
• [] My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[buuhuu]

covered by #1271