docs(pt): update content inside `pt/index.md` and `i18n/pt-PT.js`

[nazarepiedady]

Since I now have carte blanche to update the content of the Portuguese translation, I will send requests for updates larger than this one with several Markdown files changed.

If you're reading this description, and you're informed about the completion of the Portuguese content, then you may know that you can combine these changes without the reviewer's approval.

I'm their main author, as I'm also the main author of various Portuguese translations of Vue ecosystem tools, such as pt.vuejs.org and pt.vitejs.dev.

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🔨 Latest commit	37e2ff919b94e613652523895a56e8726dfdb0d0

[nazarepiedady]

@danielroe, @Atinux, @alexchopin, @smarroufin, do you have some little time to merge these updates?