feat: Documentation and API reference (#348)

Co-authored-by: Vadim Smirnov <smirnou.vadzim@gmail.com>
Co-authored-by: zakariasaad <zakaria.elas@gmail.com>
Co-authored-by: Vilfred Sikker <vilfredsikker@gmail.com>
Co-authored-by: Kasper <kasper@medusa-commerce.com>
Co-authored-by: Sebastian Rindom <skrindom@gmail.com>
Co-authored-by: Kasper Fabricius Kristensen <45367945+kasperkristensen@users.noreply.github.com>

www/docs/src/components/Intro/Intro.js

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+import React from "react"
+import Link from "@docusaurus/Link"
+import CodeBlock from "@theme/CodeBlock"
+import styles from "./intro.module.css"
+
+const Intro = ({ title, desc }) => {
+  return (
+    <div>
+      <h1 className="margin-bottom--xs margin-top--lg">Documentation</h1>
+      <p className={styles.title}>{title}</p>
+      <h2 className="margin-top--lg margin-bottom--sm">Quickstart</h2>
+      <p className={styles.description}>{desc}</p>
+      <CodeBlock>
+        {`yarn global add @medusajs/medusa-cli
+medusa new my-awesome-store`}
+      </CodeBlock>
+      <div>
+        <Link
+          to="quickstart/quick-start"
+          className="margin-top--md margin-bottom--sm button button--lg button--primary"
+        >
+          Quickstart Guide →
+        </Link>
+      </div>
+      <div className={` margin-top--md`}>
+        <Link
+          to="tutorial/set-up-your-development-environment"
+          className={`${styles.docsLink}`}
+        >
+          Set up your own local environment →
+        </Link>
+      </div>
+      <div className={`margin-top--md`}>
+        <Link
+          to="tutorial/creating-your-medusa-server"
+          className={`${styles.docsLink}`}
+        >
+          Create your very own Medusa server →
+        </Link>
+      </div>
+      <div className={`margin-top--md margin-bottom--xl`}>
+        <Link to="how-to/plugins" className={`${styles.docsLink}`}>
+          Explore plugins →
+        </Link>
+      </div>
+    </div>
+  )
+}
+
+export default Intro

www/docs/src/components/Intro/index.js

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+export { default as Intro } from "./Intro"

www/docs/src/components/Intro/intro.module.css

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+.title {
+  font-size: 24px;
+}
+
+.description {
+  font-size: 20px;
+}
+
+.docsLink {
+  font-size: 20px;
+}
+
+@media screen and (max-width: 966px) {
+  .docsLink {
+    font-size: 16px;
+  }
+}