Add Xamarin tvOS troubleshooting

[lucas-zimerman]

*The tvOS troubleshooting was added to document this case: getsentry/sentry-xamarin#59

• iOS troubleshooting got more detailed steps, due to the problem resulting in another type of error message, but also, trying to be more detailed since some users seem to not follow correctly the previous troubleshooting.

[vercel]

This pull request is being automatically deployed with Vercel (learn more).
To see the status of your deployment, click below or on the icon next to each commit.

🔍 Inspect: https://vercel.com/sentry/sentry-docs/ABkhA177HRmW7uDSVHLBFZqxXrrY
✅ Preview: https://sentry-docs-git-fork-lucas-zimerman-ref-tvos-trouble.sentry.dev