Document instructions how to rename a package

There are some pre-existing instructions [here](https://github.com/dbt-labs/hub.getdbt.com/blob/6bbfa28f39bf786aeff5376bc3fe88790b3765a0/README.md?plain=1#L9-L19), 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:
- https://github.com/dbt-labs/hubcap/issues/283

### Example

1. [Original `dbt_package.yml` file](https://github.com/CerebriumAI/airbyte_dbt_github/blob/045a94ca6da5ba425e79ecb7750c1485da23137d/dbt_project.yml) created within a GitHub repo named `CerebriumAI/airbyte_dbt_github`
- github org name: CerebriumAI
- github repo name: airbyte_dbt_github
- dbt package name: [github](https://github.com/CerebriumAI/airbyte_dbt_github/blob/045a94ca6da5ba425e79ecb7750c1485da23137d/dbt_project.yml#L5)
1. [Repo for package added to `hub.json`](https://github.com/dbt-labs/hubcap/pull/109/files)
- github org name: CerebriumAI
- github repo name: airbyte_dbt_github
1. [Changed dbt package name from `github` to `airbyte_github`](https://github.com/CerebriumAI/airbyte_dbt_github/commit/c390106e17e54cc333f58c96e3e14763cbe88893)
- github org name: CerebriumAI
- github repo name: airbyte_dbt_github
- dbt package name: **airbyte_github**
1. [Updated `data/blocklist.json` and `data/packages/ORG_NAME/OLD_PACKAGE_NAME/index.json` to redirect to new dbt package name](https://github.com/dbt-labs/hub.getdbt.com/pull/1539/files)