docs: mentioned --auto Automatic Mode (#1795)

## PR Checklist

- [x] Addresses an existing open issue: fixes #1123
- [x] That issue was marked as [`status: accepting
prs`](https://github.com/JoshuaKGoldberg/create-typescript-app/issues?q=is%3Aopen+is%3Aissue+label%3A%22status%3A+accepting+prs%22)
- [x] Steps in
[CONTRIBUTING.md](https://github.com/JoshuaKGoldberg/create-typescript-app/blob/main/.github/CONTRIBUTING.md)
were taken

## Overview

Mentions `--auto` at the bottom of `Options.md` as described.

Touches up wording to say "offline _manner_" - since _"mode"_ refers to
`--mode`.

💖

docs/Options.md

@@ -148,9 +148,21 @@ For example, providing all local change skip flags:
 npx create-typescript-app --skip-removal --skip-restore --skip-uninstall
 ```
 
+## Automatic Mode
+
+You can run `create-typescript-app` in an "automatic" manner with `--auto` and `--mode migrate`.
+Doing so will:
+
+- Use the default inference for all options
+- Bail out if any required [core options](#core-options) are missing
+
+```shell
+npx create-typescript-app --auto --mode migrate
+```
+
 ## Offline Mode
 
-You can run `create-typescript-app` in an "offline" mode with `--offline`.
+You can run `create-typescript-app` in an "offline" manner with `--offline`.
 Doing so will:
 
 - Enable `--exclude-all-contributors-api` and `--skip-github-api`