In China, set export GOPROXY=https://goproxy.cn cause some subtle reasons
the package tour include some code of a tour of go: https://tour.golang.org
the other package include tutorial of official website https://golang.org/doc/
some other code from effective go
a tour of go
Getting started
add code to print hello world
effective go
if we want to import from third-party dependency, we should use go mod go mode tidy will find and download.