home page fix (#551)

* explicit site.url in config

* infra for custom css

* moves home item to html layout

* adds baseurl to site config

docs/_config.yml

@@ -1,9 +1,8 @@
 theme: jekyll-theme-cayman
 show_downloads: false
+baseurl: /cellxgene
 
 nav:
-  - title: Home
-    url: /
   - title: Data
     url: data.html
   - title: FAQ

docs/_layouts/default.html

@@ -25,6 +25,7 @@
       <h1 class="project-name">{{ site.title | default: site.github.repository_name }}</h1>
       <h2 class="project-tagline">{{ site.description | default: site.github.project_tagline }}</h2>
       {% if site.nav %}
+        <a href="{{ site.baseurl }}/" class="btn">Home</a>
         {% for item in site.nav %}
           <a href="{{ item.url }}" class="btn">{{ item.title }}</a>
         {% endfor %}

docs/assets/css/style.scss

@@ -0,0 +1,4 @@
+---
+---
+
+@import "{{ site.theme }}";