docs: small improvement to first customization guide

[shahednasser]

Added a bit more context and what you'll build in the first customization guide and why it's powerful.

Closes DX-1044

[vercel]

The latest updates on your projects. Learn more about Vercel for Git ↗︎

Name	Status	Preview	Comments	Updated (UTC)
api-reference	🔄 Building (Inspect)	Visit Preview	💬 Add feedback	Oct 28, 2024 2:32pm
api-reference-v2	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Oct 28, 2024 2:32pm
docs-ui	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Oct 28, 2024 2:32pm
docs-v2	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Oct 28, 2024 2:32pm
medusa-dashboard	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Oct 28, 2024 2:32pm
resources-docs	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Oct 28, 2024 2:32pm

1 Skipped Deployment

Name	Status	Preview	Comments	Updated (UTC)
medusa-docs	⬜️ Ignored (Inspect)	Visit Preview		Oct 28, 2024 2:32pm

[changeset-bot]

⚠️ No Changeset found

Latest commit: a7ea95b

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

This PR includes no changesets

When changesets are added to this PR, you'll see the packages that this PR includes changesets for and the associated semver types

Click here to learn what changesets are, and how to add one.

Click here if you're a maintainer who wants to add a changeset to this PR