update usage for goenv
Merge pull request #10 from yuki-takeichi/usage_goenv

Update usage for goenv
change goenv git repository url

change goenv git repository url from wfarr/goenv to dataich/goenv.
Golang binary download location have been changed, but wfarr/goenv is not maintained.
Merge pull request #11 from dataich/master

change goenv git repository url
My envs.