Elaborate Contract Basics based on new developer experience

[ghost]

This pull request includes changes to the contract-basics.md file, which generates the documentation page titled Smart Contract Basics. Here's a summary of the modifications:

1. I have revised the language used in the section introducing the greetings smart contract. The wording is now more formal and easier to follow.
2. I've added additional text to the testing section of the contract basics to enhance readability.
3. I've removed extraneous code from the test-zoe-hello.js file, specifically code unrelated to the greetings smart contract. To maintain existing links and references, I've preserved the original file without alterations. Additionally, I've created a new file named test-zoe-01-hello.js, which will be used in the contract basics documentation.
4. The docs in the first part of contract-basics links/makes references to only test-zoe-01-hello.js file.

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[ghost]

@dckc I think I have taken care of most of your comments on this PR. Please review when you get time. Thanks.