Add Vercel Integration Docs

[ceorourke]

Add documentation for the Vercel integration.

[scefali]

@ceorourke Wondering if it makes more sense to have the docs send them directly to https://vercel.com/integrations/sentry/add since that's where we send them anyways. It will reduce the number of steps by two.

[ceorourke]

@ceorourke Wondering if it makes more sense to have the docs send them directly to https://vercel.com/integrations/sentry/add since that's where we send them anyways. It will reduce the number of steps by two.

@scefali what do you think about showing both? I'm not sure if users go to the docs first or the integration directory first.

[scefali]

@ceorourke Hmmm...I think having two sets of instructions would be confusing. My thought is that if they are already in the integration directory, they will end up finding the Vercel integration and going to the marketplace link that we show. However, if they are trying to install it while looking at the docs there's a good chance they wouldn't even have Sentry open. I'm OK with leaving it as is to be consistent with the others if you'd prefer it.

[ceorourke]

Also, do not merge until API-1076 is completed.

[MimiDumpling]

🌻 Thanks for updating the docs!

[scefali]

@ceorourke Why is there an extra line here?

[ceorourke]

I wanted to make them visually separate because the first 3 bullet points address the case where you're brand new to using sentry and sentry-webpack-plugin but have a Vercel project whereas the final one addresses the case where you already have sentry and sentry-webpack-plugin integrated. I was trying to keep it not long winded, but would it be more clear if I added some bold text indicating which situation you may fall into?

[scefali]

LGTM except for that one extra line