[docs-revamp] - Fix links (#24353)

## Summary & Motivation

This PR fixes a few busted links that were preventing Vercel deploys
from succeeding.

## How I Tested These Changes

## Changelog

NOCHANGELOG

docs/docs-beta/docs/getting-started/installation.md

@@ -72,4 +72,4 @@ If you encounter any issues during the installation process:
 ## Next steps
 
 - Get up and running with your first Dagster project in the [Quickstart](/getting-started/quickstart)
-- Learn to [create data assets in Dagster](/guides/data-modeling/data-assets)
+- Learn to [create data assets in Dagster](/guides/data-assets)

docs/docs-beta/docs/guides/external-assets.md

@@ -26,7 +26,7 @@ Examples of external assets could be files in a data lake that are populated by
 
 To follow the steps in this guide, you'll need:
 
-- A basic understanding of Dagster and assets. See the [Quick Start](/tutorial/quick-start) tutorial for an overview.
+- A basic understanding of Dagster and assets. See the [Quick Start](/getting-started/quickstart) tutorial for an overview.
 - Familiarity with [Sensors](/guides/sensors)
 </details>
 

docs/docs-beta/sidebars.ts

@@ -5,7 +5,7 @@ const sidebars: SidebarsConfig = {
       type: 'category',
       label: 'Getting Started',
       collapsed: false,
-      items: ['intro', 'getting-started/quickstart', 'tutorial/installation'],
+      items: ['intro', 'getting-started/quickstart', 'getting-started/installation'],
     },
     {
       type: 'category',