Update README.md

[eric-burel]

Add a word about HTML preview activation.
Maybe we could add why it is disabled by default (for security reasons I guess?)

Closes #98

[yhatt]

Maybe we could add why it is disabled by default (for security reasons I guess?)

Yes, it would be better. Default preference should be keeping safe from script injections by untrusted Markdown.

[yhatt]

Cool. Thanks you for contribution. 👍

[isaacdevlugt]

I'd like to enable HTML code in Marp for VS Code. How do I do this? I'm not sure what is meant by "You can enable previsualization of HTML code within Marp Markdown with the markdown.marp.enableHtml option", as stated in the README.

[yhatt]

@isaacdevlugt Marp team does not recommend to enable HTML, for saving average users like you from some malicious. Enabling HTML is for the advanced user, and especially should take care if you could not recognize a meaning.

You have to learn how to be setting in VS Code at https://code.visualstudio.com/docs/getstarted/settings#_creating-user-and-workspace-settings. To enable "Markdown > Marp: Enable HTML" in setting GUI means exactly same as enabling markdown.marp.enableHtml in setting by JSON.

Our docs won't explain about VS Code built-in features to avoid confusion about the feature of our extension.