Release instructions (#136)

* Instructions for releasing prod application to Heroku

* Include initial instructions for configuring an automated release process

RELEASE.md

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+# Release instructions
+
+This application is hosted on [Heroku](https://www.heroku.com), but it can also be executed in production mode locally.
+
+## Design overview
+It is designed to do the following:
+1. Use a cron schedule to execute the `cron.sh` script at the beginning of every hour
+    1. The `cron.sh` script creates a `git-tmp` directory that is destroyed upon completion
+2. The `cron.sh` script defers most of the processing to `hubcap.py`
+3. `hubcap.py` creates a JSON spec file for each package+version combo within the `git-tmp/hub/data/packages/` directory
+4. It opens pull requests against [dbt-labs/hub.getdbt.com](https://github.com/dbt-labs/hub.getdbt.com) for any new versions of dbt packages
+    - [Example PR for first-time package](https://github.com/dbt-labs/hub.getdbt.com/pull/1681/files)
+    - [Example PR for new version of existing package](https://github.com/dbt-labs/hub.getdbt.com/pull/1683/files)
+
+## Heroku production setup
+
+The commands below assume a production application named `dbt-hubcap`. Replace with `dbt-hubcap-staging` for the staging version of the application.
+
+1. Use the [Heroku Scheduler](https://dashboard.heroku.com/apps/dbt-hubcap/scheduler) to set the following cron schedule:
+    - Job: `./cron.sh`
+    - Schedule: Every hour at :00
+    - Dyno size: Hobby / Standard-1X
+1. Configure the `CONFIG` and `ENV` environment variables: [Settings > Config Vars > Reveal Config Vars](https://dashboard.heroku.com/apps/dbt-hubcap/settings)
+    - `CONFIG`: copy format from `config.example.json` and adjust values as needed
+    - `ENV`: `prod`
+1. (Re-)deploy the application using the instructions below. See [these](https://dashboard.heroku.com/apps/dbt-hubcap/deploy/heroku-git) instructions for context.
+
+
+## Heroku production release (automated)
+
+It is possible to configure automatic deploys from GitHub to deploy automatically whenever a specific branch is pushed to: [Deploy > Deployment method > GitHub > Connect to GitHub](https://dashboard.heroku.com/apps/dbt-hubcap/deploy/github).
+
+## Heroku production release (manual)
+
+All of the following steps can be performed locally to initiate a remote deploy on Heroku.
+
+### Install the Heroku CLI
+Download and install the [Heroku CLI](https://devcenter.heroku.com/articles/heroku-command-line).
+
+If you haven't already, log in to your Heroku account and follow the prompts to create a new SSH public key.
+
+```shell
+heroku login
+```
+
+### Deploy
+
+To deploy or re-deploy the latest changes:
+```shell
+git clone [email protected]:dbt-labs/hubcap.git
+cd hubcap
+git pull origin
+git checkout main
+heroku git:remote -a dbt-hubcap
+git push heroku main:main
+```
+
+#### Explanation
+
+`heroku` is the remote that Heroku will use for deploys. `origin` is the source code hosted on GitHub.
+
+Pulling from `origin` will get the latest code in GitHub. Pushing to `heroku` will deploy that latest code to the Heroku app.
+
+You can use the following command to list the tracked repositories:
+```shell
+git remote -v
+```
+
+The result should be something like the following:
+```
+heroku  https://git.heroku.com/dbt-hubcap.git (fetch)
+heroku  https://git.heroku.com/dbt-hubcap.git (push)
+origin  [email protected]:dbt-labs/hubcap.git (fetch)
+origin  [email protected]:dbt-labs/hubcap.git (push)
+```