docs: Example Suspicious Activity Report (FinCEN SAR) (FinCEN Report 111)

[adamdecaf]

On our docs site let's have a page showing an example SAR report. It can include sample values and code. A full Go example would be ideal.

https://github.com/moov-io/fincen/blob/main/suspicious_activity/activity.go

[mfdeveloper508]

#22