docs: add Mappia to README

[damienwebdev]

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[what-the-diff]

PR Summary

• Addition of an "Alternatives" Section
  A new section called "Alternatives" has been added to the README.md file. This should help users get a broader understanding of the different options available to meet their needs.

• Inclusion of "Mappia" subsection
  We have introduced a subsection that talks about "Mappia". It is highlighted as a robust tool for deploying and managing Magento, a popular eCommerce platform, in a Kubernetes environment. This update provides users with valuable information about this alternative, which could be highly beneficial for their production-grade workloads.