Document that Tea extension is a collection of best practices

[lukaszuznanski]

As the Tea example is not a best practice example in itself (with all the tools in it), but a collection of best practices. So we should document this to our Tea extension README and the extension manual. (Note: The minimal example will be auto-created from the CPS project builder template in the future.)

Document in the README and the docs that the Tea example is an opiniated example recommended best practices, and that is does not serve as a source for official requirements for TYPO3 extensions.