Create _prose.yml

仮だけど、とりあえず必要な要素を書いた
Merge pull request #16 from blanketsheep/dev/prose

Create _prose.yml
Create .gitkeep

やってなかったみたい
Merge pull request #18 from blanketsheep/dev/prose

Create .gitkeep
Merge remote-tracking branch 'origin/develop' into design/0509