Setting up dojo.io locally fails build

`npm run build` fails because `db.json` does not exist. You need to `touch site/db.json` to fix.

But it still doesn't run, so you can get around that manually by `cd site && hexo clean && hexo build`.

Either we need to fix the build process or update the README file with proper instructions.

Start by reproducing `npm run build`, then inspect the setup involving `site/db.json` and compare it with `cd site && hexo clean && hexo build`. Check the README instructions and the build process; done means a documented or automated setup that builds successfully without the manual workaround.

Written by the indexing model from the issue text.