Update docs to include the description of what legacy actually does for @babel/plugin-proposal-decorators

[catamphetamine]

The docs are very vague about legacy flag on @babel/plugin-proposal-decorators.
They don't tell which one should a developer choose: legacy: false or legacy: true.
There is no description of the actual difference in behaviour whether the flag is enabled or disabled.
https://babeljs.io/docs/en/next/babel-plugin-proposal-decorators.html

[babel-bot]

Hey @catamphetamine! We really appreciate you taking the time to report an issue. The collaborators
on this project attempt to help as many people as possible, but we're a limited number of volunteers,
so it's possible this won't be addressed swiftly.

If you need any help, or just have general Babel or JavaScript questions, we have a vibrant Slack
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[nicolo-ribaudo]

As for now, only legacy: true is supported so it doesn't really make sense to explain the difference. We will publish a detailed blog post about this when we will support legacy: false.

[babel-bot]

Hey @catamphetamine! We really appreciate you taking the time to report an issue. The collaborators
on this project attempt to help as many people as possible, but we're a limited number of volunteers,
so it's possible this won't be addressed swiftly.

If you need any help, or just have general Babel or JavaScript questions, we have a vibrant Slack
community that typically always has someone willing to help. You can sign-up here
for an invite.