add link to github in demo site

Author: beenotung

src/DemoApp.tsx

@@ -19,6 +19,21 @@ function DemoApp() {
             src="https://img.shields.io/npm/v/react-use-storage-state.svg"
             alt="npm package version badge"
           ></img>
+        </a>{' '}
+        <a href="https://github.com/beenotung/react-use-storage-state">
+          <svg
+            height="32"
+            aria-hidden="true"
+            viewBox="0 0 16 16"
+            version="1.1"
+            width="32"
+            data-view-component="true"
+          >
+            <path
+              fill-rule="evenodd"
+              d="M8 0C3.58 0 0 3.58 0 8c0 3.54 2.29 6.53 5.47 7.59.4.07.55-.17.55-.38 0-.19-.01-.82-.01-1.49-2.01.37-2.53-.49-2.69-.94-.09-.23-.48-.94-.82-1.13-.28-.15-.68-.52-.01-.53.63-.01 1.08.58 1.23.82.72 1.21 1.87.87 2.33.66.07-.52.28-.87.51-1.07-1.78-.2-3.64-.89-3.64-3.95 0-.87.31-1.59.82-2.15-.08-.2-.36-1.02.08-2.12 0 0 .67-.21 2.2.82.64-.18 1.32-.27 2-.27.68 0 1.36.09 2 .27 1.53-1.04 2.2-.82 2.2-.82.44 1.1.16 1.92.08 2.12.51.56.82 1.27.82 2.15 0 3.07-1.87 3.75-3.65 3.95.29.25.54.73.54 1.48 0 1.07-.01 1.93-.01 2.2 0 .21.15.46.55.38A8.013 8.013 0 0016 8c0-4.42-3.58-8-8-8z"
+            ></path>
+          </svg>
         </a>
       </p>
       <p>