add site metadata component for useStaticQuery

Author: spences10

src/components/SiteMetadata.js

@@ -0,0 +1,19 @@
+import { graphql, useStaticQuery } from 'gatsby'
+
+const useSiteMetadata = () => {
+  const { site } = useStaticQuery(
+    graphql`
+      query SITE_METADATA_QUERY {
+        site {
+          siteMetadata {
+            title
+            description
+          }
+        }
+      }
+    `
+  )
+  return site.siteMetadata
+}
+
+export default useSiteMetadata