Add link to the demo in navigation bar and README (#1564)

* Add link to the demo in navigation bar

* Add link to the demo in README

website/pages/index.html

@@ -27,7 +27,7 @@
         <a href="docs/api.html" role="button"><i class="fa fa-book"></i> Documentation</a>
         <a href="https://github.com/Khan/KaTeX" role="button"><i class="fa fa-github"></i> View on GitHub</a>
       </div>
-      <div class="demo">
+      <div class="demo" id="demo">
         <div class="demo-left">
           <div class="demo-instructions">
             <label for="demo-input">Type an expression:</label>

website/siteConfig.js

@@ -33,6 +33,7 @@ const siteConfig = {
     organizationName: 'Khan',
 
     headerLinks: [
+        {href: baseUrl + '#demo', label: 'Try'},
         {doc: 'node', label: 'Docs'},
         {page: 'users', label: 'Users'},
         {href: 'https://github.com/Khan/KaTeX', label: 'GitHub'},