Installing packages manually

go install: no install location for directory E:\...\...\src outside GOPATH

        For more details see: 'go help gopath'

Install the defined package automatically

Need to check the GOPATH directory first which is complicated..
Make sure that GOPATH is applied to current Go project
go get

Install the defined package manually

Can just call go install github.com/gorilla/mux to install your desire package