Update guidance on development environment seed data.

Relates to [this proposal][1] for Suspenders.

> We have relied on [`dev:prime`][2] for loading data necessary for users
to view most of the features of the app in development.
>
> However, there were a few areas of improvement.
>
> First, rename `dev` namespace to `development`, and rename
[`prime`][1] task to `seed` for improved clarity.
>
> The, introduces `development:seed:replant` take to create parity with
the existing `db:seed:replant` task.

[1]: thoughtbot/suspenders#1251
[2]: https://thoughtbot.com/blog/priming-the-pump

Author: stevepolitodesign

rails/README.md

@@ -43,7 +43,7 @@
 - Validate the associated `belongs_to` object (`user`), not the database column
   (`user_id`).
 - Use `db/seeds.rb` for data that is required in all environments.
-- Use `dev:prime` rake task for development environment seed data.
+- Use `development:seed` rake task for development environment seed data.
 - Prefer `cookies.signed` over `cookies` to [prevent tampering].
 - Prefer `Time.current` over `Time.now`
 - Prefer `Date.current` over `Date.today`