Change mentions of introduction.mdx to index.mdx (#868)

Author: mycho2003

quickstart.mdx

@@ -107,9 +107,9 @@ pnpm add -g mint
 
 After you set up your environment, you can start editing your documentation files. For example, update the title of the introduction page:
 
-Open your repository created during onboarding, find the `introduction.mdx` file, and find the top of the file:
+Open your repository created during onboarding, find the `index.mdx` file, and find the top of the file:
 
-```mdx introduction.mdx
+```mdx index.mdx
 ---
 title: "Introduction"
 description: "This is the introduction to the documentation"
@@ -118,7 +118,7 @@ description: "This is the introduction to the documentation"
 
 Update the `title` field to `"Hello World"`.
 
-```mdx introduction.mdx {2}
+```mdx index.mdx {2}
 ---
 title: "Hello World"
 description: "This is the introduction to the documentation"
@@ -174,7 +174,7 @@ The web editor workflow provides a what-you-see-is-what-you-get (WYSIWYG) interf
 
 In the web editor, you can navigate through your documentation files in the sidebar. Let's update the introduction page:
 
-Find and select `introduction.mdx` in the file explorer.
+Find and select `index.mdx` in the file explorer.
 
 Then, in the editor, update the title field to "Hello World".