[Aug 24, 2021] Top level CLI docs set (#20628)

Co-authored-by: Ethan Palm <56270045+ethanpalm@users.noreply.github.com>
Co-authored-by: Mislav Marohnić <mislav@github.com>
Co-authored-by: Laura Coursen <lecoursen@github.com>

content/github-cli/github-cli/quickstart.md

@@ -0,0 +1,46 @@
+---
+title: GitHub CLI quickstart
+intro: 'Start using {% data variables.product.prodname_cli %} to work with {% data variables.product.company_short %} in the command line.'
+versions:
+  fpt: '*'
+  ghes: '*'
+  ghae: '*'
+topics:
+  - CLI
+type: overview
+allowTitleToDifferFromFilename: true
+shortTitle: Quickstart
+---
+
+## About {% data variables.product.prodname_cli %}
+
+{% data reusables.cli.about-cli %}
+
+## Getting started
+
+1. [Install](https://github.com/cli/cli#installation) {% data variables.product.prodname_cli %} on macOS, Windows, or Linux.
+1. In the command line, authenticate to {% data variables.product.company_short %}.
+
+  ```shell
+  gh auth login
+  ```
+
+  {% ifversion not fpt %}
+  To authenticate to {% data variables.product.product_location %}, use the `--hostname` flag.
+
+  ```shell
+  gh auth login --hostname <em>hostname</em>
+  ```
+
+  {% endif %}
+1. Start working with {% data variables.product.company_short %} in the command line. For example, find an issue to work on with `gh issue status` or `gh issue list --assignee @me`. Create a pull request with `gh pr create`. Review a pull request with `gh pr checkout`, `gh pr diff` and `gh pr review`.
+
+## Next steps
+
+- Tell {% data variables.product.prodname_cli %} which text editor to use for commands that open a text editor. For example, enter `gh config set editor "code -w"` to set your preferred text editor to {% data variables.product.prodname_vscode %}. For more information, see [`gh config set`](https://cli.github.com/manual/gh_config_set).
+
+- Define aliases for commands that you commonly run. For example, if you run `gh alias set prd "pr create --draft"`, you will then be able to run `gh prd` to quickly open a draft pull request. For more information, see [`gh alias`](https://cli.github.com/manual/gh_alias).
+
+- Create or add custom commands with {% data variables.product.prodname_cli %} extensions. For more information, see "[Using {% data variables.product.prodname_cli %} extensions](/github-cli/github-cli/using-github-cli-extensions)" and "[Creating {% data variables.product.prodname_cli %} extensions](/github-cli/github-cli/creating-github-cli-extensions)."
+
+- For more information about all of the commands that you can run with {% data variables.product.prodname_cli %}, see "[{% data variables.product.prodname_cli %} reference](/github-cli/github-cli/github-cli-reference)."