Update the mini guide to creating archectypes to Archetype 2.x

as noticed by a user recently, the mini-guide "Guide to Creating Archetypes" explains about Archetype 1.x which is deprecated in favor of Archetype 2.x:

• Archetype 1.x used archetype.xml descriptor: https://maven.apache.org/archetype/archetype-common/archetype.html
• Archetype 2.x uses a different descriptor archetype-metadata.xml with a different schema : https://maven.apache.org/archetype/archetype-models/archetype-descriptor/archetype-descriptor.html

there may be other differences when upgrading from Archetype 1 to Archetype 2, I did not investigate in details