Git：fatal: ‘upstream‘ does not appear to be a git repositoryfatal: Could not read from remote repos

• 具体命令与错误

$ git fetch upstream
fatal: 'upstream' does not appear to be a git repository
fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists.      

• 原因

• 解决办法

$ git remote add upstream https://github.com/openjdk/jdk8u

$ git fetch upstream