yarn install package from github

yarn add https://github.com/fancyapps/fancybox [remote url]
yarn add ssh://github.com/fancyapps/fancybox#3.0  [branch]
yarn add https://github.com/fancyapps/fancybox#5cda5b529ce3fb6c167a55d42ee5a316e921d95f [commit]
yarn add <git remote url> installs a package from a remote git repository.
yarn add <git remote url>#<branch/commit/tag> installs a package from a remote git repository at specific git branch, git commit or git tag.
yarn add https://my-project.org/package.tgz installs a package from a remote gzipped tarball.