Add Docker installation instructions to get started guide (#112)

* Initial plan

* Add Docker installation instructions to get started guide

Co-authored-by: hawkeyexl <[email protected]>

* Add cross-platform Docker commands for Windows, macOS, and Linux

Co-authored-by: hawkeyexl <[email protected]>

* Add inline test statements for Docker installation procedure

Co-authored-by: hawkeyexl <[email protected]>

* Simplify Docker installation: remove docker pull, use single command with . for current directory

Co-authored-by: hawkeyexl <[email protected]>

* Change Docker mount path to /app and add NPX vs Docker selection guidance

Co-authored-by: hawkeyexl <[email protected]>

* Update index.mdx

* Update index.mdx

---------

Co-authored-by: copilot-swe-agent[bot] <[email protected]>
Co-authored-by: hawkeyexl <[email protected]>
Co-authored-by: Manny Silva <[email protected]>

Author: Copilot

docs/get-started/installation/index.mdx

@@ -4,10 +4,17 @@ sidebar_label: Installation
 
 import spec from "./sample.spec.json";
 import CodeBlock from '@theme/CodeBlock';
+import Tabs from '@theme/Tabs';
+import TabItem from '@theme/TabItem';
 
 # Installation
 
-Downloading and running Doc Detective is straightforward. Follow these steps to install Doc Detective and run your first test:
+Downloading and running Doc Detective is straightforward. You can install Doc Detective using NPX (Node.js) or Docker. Follow the instructions for your preferred method:
+
+Choose *NPX* if you have Node.js installed and want to install Doc Detective on your machine locally. Choose *Docker* if you can't install applications locally, prefer containerized environments, need to avoid Node.js installation, or want to isolate Doc Detective from your system.
+
+<Tabs>
+  <TabItem value="npx" label="NPX" default>
 
 1. Install prerequisites:
 
@@ -41,6 +48,37 @@ Downloading and running Doc Detective is straightforward. Follow these steps to
     command: "npx doc-detective --input sample.spec.json"
     workingDirectory: "." */}
 
+  </TabItem>
+  <TabItem value="docker" label="Docker">
+
+1. Install prerequisites:
+
+    - [Docker](https://docs.docker.com/get-docker/)
+    {/* step checkLink: "https://docs.docker.com/get-docker/" */}
+
+2. Save this file to your current directory as _sample.spec.json_:
+
+    <CodeBlock language="json" title="sample.spec.json">
+      {JSON.stringify(spec, null, 2)}
+    </CodeBlock>
+
+3. Run a test, pointing to the file you just created:
+
+    <CodeBlock language="bash" title="Run test">
+      docker run -v .:/app docdetective/docdetective --input /app/sample.spec.json
+    </CodeBlock>
+    {/* step runShell:
+    command: "docker run -v .:/app docdetective/docdetective --input /app/sample.spec.json"
+    workingDirectory: "." */}
+
+    :::note
+
+    The `-v` argument mounts your current directory (`.`) to `/app` in the container, giving Doc Detective access to your test specification and enabling it to output results and screenshots. If your test specification is hosted at an HTTPS URL, the `-v` argument is not necessary.
+
+    :::
+
+  </TabItem>
+</Tabs>
 
 Congratulations! You've run your first test with Doc Detective. :tada: