Add a presentation of Plume and of the instance on the homepage

Fixes #132

migrations/2018-07-27-194816_instance_description_html/down.sql

@@ -0,0 +1,3 @@
+-- This file should undo anything in `up.sql`
+ALTER TABLE instances DROP COLUMN long_description_html;
+ALTER TABLE instances DROP COLUMN short_description_html;

migrations/2018-07-27-194816_instance_description_html/up.sql

@@ -0,0 +1,3 @@
+-- Your SQL goes here
+ALTER TABLE instances ADD COLUMN long_description_html VARCHAR NOT NULL DEFAULT '';
+ALTER TABLE instances ADD COLUMN short_description_html VARCHAR NOT NULL DEFAULT '';