Docs team edits

[zuluecho9]

This is from Zach Elwood on NR docs team.

This PR is to add a ‘how to find data’ section so that customers can find the data they send. I’ve included what I think are the applicable data types (spans and metrics) but let me know if there are other data types reported by this exporter. If you think this exporter will change to send other types of data in future, keep in mind it will be important to update this repo with link to that data type.

Also changed some instances of title case to sentence case; small thing but we want headings to be sentence case and not title case, so just something to keep in mind when creating new content. Let me know if you think I changed sentence case stuff that shouldn't have been changed.

Also changed from 'Use Insights' to 'Use NRQL'. We want to avoid instances of Insights because we want to promote NR1 chart builder, or just mention NRQL for specific NRQL use cases.

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