Squashed '_emacs.d/' changes from 40eae6c..bd46a9a

bd46a9a Fix install instruction: add `cask install`

git-subtree-dir: _emacs.d
git-subtree-split: bd46a9ad87d81ccf255f8e9985ed5cc1db548860
Merge commit '46ddb70e4b81eddc26dc56c06b807aa9fd670b4f'