Analytics docs improvements

[lobsterkatie]

As a dev just starting to use our analytics tools, here are a few things the docs at https://develop.sentry.dev/analytics/ left me wondering, which it'd be great if we could add:

• How do you decide whether to send data to reload or amplitide (or both)? What is each good for? What are some examples?
• Okay, great, I sent some data. Where/how do I go find it?