Update development-guide to include installation of `Terraform`

# 💡 Summary #

We should include manual installation steps for [Terraform](https://www.terraform.io/).

## Motivation and context ##

Why does this work belong in this project?

Right now unless you run the [laptop script](https://github.com/cisagov/laptop) instructed in the [mac-env-setup ](https://github.com/cisagov/development-guide/blob/develop/dev_envs/mac-env-setup.md) users won't have [TF](https://www.terraform.io/) installed on their systems. This could lead to some issues if they attempt to work any TF related project. The version should be pinned to the version specified in [cisagov/setup-env-github-action](https://github.com/cisagov/setup-env-github-action).

## Acceptance criteria ##

- [ ] Development guide includes steps of how to manually install TF.