feat(v2): improve seo (#1588)

* feat(v2): improve seo

- Add doc specific seo information
- Add twitter meta tags to seo in theme Layout

* Cannot use svg in SEO image

* Add docs about SEO

* add site default image for seo

* Resolve PR discussion

* Add `image` to config optional fields

* Use theme config instead of root config for image, rename in front matter

* Use absolute url for image (wont work on preview)

* update docs for frontmatter field for seo

* refactor

* pages seo

* fix

* nits again'

website/src/pages/feedback/index.js

@@ -23,7 +23,7 @@ function Feedback() {
   }, []);
 
   return (
-    <Layout>
+    <Layout permalink={'/feedback'} description={'Docusaurus 2 Feedback page'}>
       <div className="container margin-vert--xl" data-canny />
     </Layout>
   );

website/src/pages/index.js

@@ -65,7 +65,9 @@ function Home() {
   const {siteConfig = {}} = context;
 
   return (
-    <Layout description={'Docusaurus makes it easy to build websites'}>
+    <Layout
+      permalink={'/'}
+      description={'Docusaurus makes it easy to build websites'}>
       <div className={styles['index-hero']}>
         <div className={styles['index-hero-inner']}>
           <h1 className={styles['index-hero-project-tagline']}>