Perform check that site is correctly configured

Display informative error message if user attempted to clone/download
Academic without following all the installation steps.

Close #491

layouts/index.html

@@ -1 +1,4 @@
+{{ if not (isset $.Site.Params "color_theme") }}
+  {{ errorf "Please complete the installation of Academic by following the steps at https://sourcethemes.com/academic/docs/install/" }}
+{{ end }}
 {{ partial "widget_page.html" . }}