That will merge the `.md` files in `next` into a single file.
Atomically (as close to it as possible) add that file to `_content/doc` directory
of the website repository and remove the `doc/next` directory in this repository.

To begin the next release development cycle, populate the contents of `next`
with those of `initial`. From the repo root:

    > cd doc
    > cp -r initial/* next