Merge pull request jupyter#437 from palewire/seo

Fixed SEO bugs identified by Lighthouse

Author: Carreau

_includes/head.html

@@ -3,14 +3,14 @@
     <meta charset="utf-8">
     <meta http-equiv="X-UA-Compatible" content="IE=edge">
     <meta name="viewport" content="width=device-width, initial-scale=1">
-    <meta name="description" content="">
-    <meta name="author" content="">
+    <meta itemprop="description" name="description" content="{% if page.tagline %}{{ page.tagline }}{% else %}{{ site.description }}{% endif %}" />
 
     <title>{{ site.title }} {% if page.title %}| {{ page.title }}{% endif %}</title>
     <meta property="og:title" content="Project Jupyter" />
     <meta property="og:description" content="{{ site.description }}">
     <meta property="og:url" content="https://www.jupyter.org" />
     <meta property="og:image" content="https://jupyter.org/assets/homepage.png" />
+    <link rel="canonical" href="{{ page.url | prepend: site.url }}">
     <!-- Bootstrap Core CSS -->
     <link rel="stylesheet" href="{{ "/css/bootstrap.min.css" | prepend: site.baseurl }}">
     <link rel="stylesheet" href="{{ "/css/logo-nav.css" | prepend: site.baseurl }}?{{site.time | date: '%s%N'}}">

_includes/header.html

@@ -37,7 +37,7 @@
                            {%- if nav contains targetpage.title -%}
                               {%- if page.title == targetpage.title %}
                                <li>
-                                   <a href  class="tab navbar-active">{{targetpage.title}}</a>
+                                   <a href="{{site.baseurl}}{{targetpage.url}}" class="tab navbar-active">{{targetpage.title}}</a>
                                </li>
                                {%- else %}
                                <li>

index.html

@@ -200,7 +200,7 @@ <h3 class="section-header">Currently in use at</h3>
                     <li class="col"><a href="https://software-carpentry.org"><img src="assets/carpentry.svg" class="greydout" alt="Carpentry"></a></li>
                     <li class="col"><a href="https://www.janelia.org/"><img src="assets/janelia.svg" class="greydout" alt="Janelia"></a></li>
                     <li class="col"><a href="https://codeneuro.org/"><img src="assets/codeneuro.svg" class="greydout" alt="CodeNeuro"></a></li>
-                    <li class="col"><a href=""><img src="assets/nsite.svg" class="greydout" alt="NSite"></a></li>
+                    <li class="col"><a href="https://www.linkedin.com/company/nsite-llc/about/"><img src="assets/nsite.svg" class="greydout" alt="NSite"></a></li>
                     <li class="col"><a href="https://cocalc.com/"><img src="assets/cocalc.svg" class="greydout" alt="CoCalc"></a></li>
                     <li class="col"><a href="https://www.brynmawr.edu"><img src="assets/brynmawr.svg" class="greydout" alt="BrynMawr"></a></li>
                     <li class="col"><a href="https://www.calpoly.edu"><img src="assets/calpoly.svg" class="greydout" alt="CalPoly"></a></li>