Add VS Code integration instructions to README

[NathanC]

I just got UdonSharp the other day, but had difficulty finding how to get Intellisence working with VS Code. Someone in the discord helped me, and I figured I'd add it to the README if there are no objections.

[github-actions[bot]]

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[NathanC]

I have read the CLA Document and I hereby sign the CLA

[NathanC]

recheck