feat(v2): Improve the initial templates (#4302)

* feat: add getting started doc at classic inital templates

* fix: improve the contents of getting started page

* fix: fix slug routing

* fix: rename gettingStarted to getting-started and re-adjust the content

* feat: add markdown-features docs

* feat: add a page on how to create a simple document

* feat: add a page on how to create pages

* feat: add create a post doc

* feat: add thank you page with whats next

* fix: reduce the content of the init templates

* update the init template

Co-authored-by: Lisa Chandra <52909743+lisa761@users.noreply.github.com>
Co-authored-by: Javid <singularity.javid@gmail.com>
Co-authored-by: slorber <lorber.sebastien@gmail.com>

packages/docusaurus-init/templates/classic/docs/create-a-blog-post.md

@@ -0,0 +1,25 @@
+---
+title: Create a Blog Post
+---
+
+This page will help you on how to create blog posts in Docusaurus.
+
+## Create a Blog Post
+
+Create a file at `blog/2021-02-28-greetings.md`:
+
+```md title="blog/2021-02-28-greetings.md"
+---
+title: Greetings!
+author: Steven Hansel
+author_title: Docusaurus Contributor
+author_url: https://github.com/ShinteiMai
+author_image_url: https://github.com/ShinteiMai.png
+---
+
+Congratulations, you have made your first post!
+
+Feel free to play around and edit this post as much you like.
+```
+
+A new blog post is now available at `http://localhost:3000/blog/greetings`.

packages/docusaurus-init/templates/classic/docs/create-a-document.md

@@ -0,0 +1,38 @@
+---
+title: Create a Document
+---
+
+Documents are pages with a **sidebar**, a **previous/next navigation** and many other useful features.
+
+## Create a Document
+
+Create a markdown file at `docs/my-doc.md`:
+
+```mdx title="docs/hello.md"
+---
+title: Hello, World!
+---
+
+## Hello, World!
+
+This is your first document in **Docusaurus**, Congratulations!
+```
+
+A new document is now available at `http://localhost:3000/docs/hello`.
+
+## Add your document to the sidebar
+
+Add `hello` to the `sidebars.js` file:
+
+```diff title="sidebars.js"
+module.exports = {
+  docs: [
+    {
+      type: 'category',
+      label: 'Docusaurus Tutorial',
+-     items: ['getting-started', 'create-a-doc', ...],
++     items: ['getting-started', 'create-a-doc', 'hello', ...],
+    },
+  ],
+};
+```

packages/docusaurus-init/templates/classic/docs/create-a-page.md

@@ -0,0 +1,45 @@
+---
+title: Create a Page
+---
+
+Any React or Markdown file created under `src/pages` directory is converted into a website page:
+
+- `src/pages/index.js` -> `localhost:3000/`
+- `src/pages/foo.md` -> `localhost:3000/foo`
+- `src/pages/foo/bar.js` -> `localhost:3000/foo/bar`
+
+## Create a React Page
+
+Create a file at `src/pages/my-react-page.js`:
+
+```jsx title="src/pages/my-react-page.js"
+import React from 'react';
+import Layout from '@theme/Layout';
+
+function HelloWorld() {
+  return (
+    <Layout>
+      <h1>My React page</h1>
+      <p>This is a React page</p>
+    </Layout>
+  );
+}
+```
+
+A new page is now available at `http://localhost:3000/my-react-page`.
+
+## Create a Markdown Page
+
+Create a file at `src/pages/my-markdown-page.md`:
+
+```mdx title="src/pages/my-markdown-page.md"
+---
+title: My Markdown page
+---
+
+# My Markdown page
+
+This is a Markdown page
+```
+
+A new page is now available at `http://localhost:3000/my-markdown-page`.

packages/docusaurus-init/templates/classic/docs/getting-started.md

@@ -0,0 +1,28 @@
+---
+title: Getting Started
+slug: /
+---
+
+## Step 1: Generate a new Docusaurus site
+
+If you haven't already, generate a new Docusaurus site using the classic template:
+
+```shell
+npx @docusaurus/init@latest init my-website classic
+```
+
+## Step 2: Start your Docusaurus site
+
+Run the development server in the newly created `my-website` folder:
+
+```shell
+cd my-website
+
+npx docusaurus start
+```
+
+Open `docs/getting-started.md` and edit some lines. The site reloads automatically and display your changes.
+
+## That's it!
+
+Congratulations! You've successfully run and modified your Docusaurus project.