Documentation sum broken image URL

[JongminChung]

There are sum broken images.

AS_IS:

• https://raw.githubusercontent.com/tanstack/tanstack.com/main/src/images/railway-light.svg

TO_BE:

• https://raw.githubusercontent.com/tanstack/tanstack.com/main/src/images/railway-white.svg or
• https://raw.githubusercontent.com/tanstack/tanstack.com/main/src/images/railway-black.svg