bflanigan: add main.go Gophercon greeting
bflanigan: add main.go Gophercon greeting

Change-Id: I348f30eb4dc750b634c4cb6be32b5eab3570480b
Reviewed-on: https://go-review.googlesource.com/48854
Reviewed-by: Han-Wen Nienhuys <3269a793d567baa2fa5b041e3e5e0a5039790a2f@google.com>

golang/scratch