Remove Nitrous installation files

doc/index.markdown

@@ -110,7 +110,6 @@ Technical details
 - [Run Kanboard with Docker](docker.markdown)
 - [Run Kanboard with Vagrant](vagrant.markdown)
 - [Run Kanboard on Cloudron](cloudron.markdown)
-- [Run Kanboard on Nitrous](nitrous.markdown)
 
 ### Configuration
 

doc/nitrous.markdown

@@ -1,10 +0,0 @@
-Nitrous Quickstart
-==================
-
-Create a free development environment for this Kanboard project in the cloud on [Nitrous.io](https://www.nitrous.io) by clicking the button below.
-
-<a href="https://www.nitrous.io/quickstart">
-  <img src="https://nitrous-image-icons.s3.amazonaws.com/quickstart.png" alt="Nitrous Quickstart" width=142 height=34>
-</a>
-
-Simply access your site via the `Preview > 3000` link in the IDE.

doc/ru_RU/index.markdown

@@ -178,7 +178,6 @@
 
 -   [Запуск Kanboard на Cloudron](cloudron.markdown)
 
--   [Запуск Kanboard на Nitrous](nitrous.markdown)
 
 
 ### Настройка[¶](#configuration "Ссылка на этот заголовок")