Rails: 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.

We're already doing this in ChatBot.

thoughtbot/chat_bot#52

[1]: thoughtbot/suspenders#1251

Author: stevepolitodesign

rails/README.md

@@ -79,7 +79,7 @@ Guidance on ActiveRecord, ActiveModel, and other model objects.
   suffixes.
 - Keep `db/schema.rb` or `db/development_structure.sql` under version control.
 - Use `db/seeds.rb` for data that is required in all environments.
-- Use `dev:prime` rake task for development environment seed data.
+- Use `development:db:seed` rake task for development environment seed data.
 
 ## Migrations