Add SEO component to HOCs and React Router pages

Author: AryanJ-NYC

src/pages/examples/hocs.mdx

@@ -4,6 +4,14 @@ route: /examples/hocs
 menu: Examples
 ---
 
+import SEO from '../../components/seo';
+
+<SEO
+  description="Using TypeScript with higher order components or HOCs."
+  title="Higher Order Components (HOCs)"
+  keywords={['higher-order components', 'higher order components', 'hocs']}
+/>
+
 # Higher Order Components (HOCs)
 
 Please note that this section uses the `utility-types` [package](https://github.com/piotrwitek/utility-types) since, as of May 2019, the helper functions were unavailable in TypeScript.

src/pages/examples/react-router.mdx

@@ -4,6 +4,20 @@ route: /examples/react-router
 menu: Examples
 ---
 
+import SEO from '../../components/seo';
+
+<SEO
+  description="Using TypeScript with React Router."
+  title="React Router"
+  keywords={[
+    'react router',
+    'router',
+    'withRouter',
+    'url parameters',
+    'route parameters',
+  ]}
+/>
+
 # React Router
 
 ## withRouter