Document instructions how to rename a package

[dbeatty10]

There are some pre-existing instructions here, but they should be more explicit, imo.

Based on https://github.com/dbt-labs/hub.getdbt.com/pull/1539/files, it looks like the process is similar to:

• Document instructions how to rename an organization #283

Example

1. Original dbt_package.yml file created within a GitHub repo named CerebriumAI/airbyte_dbt_github
   • github org name: CerebriumAI
   • github repo name: airbyte_dbt_github
   • dbt package name: github
2. Repo for package added to hub.json
   • github org name: CerebriumAI
   • github repo name: airbyte_dbt_github
3. Changed dbt package name from github to airbyte_github
   • github org name: CerebriumAI
   • github repo name: airbyte_dbt_github
   • dbt package name: airbyte_github
4. Updated data/blocklist.json and data/packages/ORG_NAME/OLD_PACKAGE_NAME/index.json to redirect to new dbt package name