Add general Vagrant documentation

docs/en/installation/vagrant.md

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+# Vagrant
+
+Install [Vagrant](https://www.vagrantup.com/) and setup a virtual machine with [Linux](prerequisites.md)
+
+Vagrant is compatible for [Debian](/en/installation/debian.md) and [Ubuntu](/en/installation/ubuntu.md).
+
+## Browser configuration
+
+To access the application through the brower at `localhost:3000` we must forward a port and run the rails server with a binding option:
+
+## Port forwarding
+Open the Vagrant configuration file:
+
+```
+nano Vagranfile
+```
+
+Find this line:
+
+```
+# config.vm.network "forwarded_port", guest: 80, host: 8080
+```
+
+And change it for this configuration:
+
+```
+config.vm.network "forwarded_port", guest: 3000, host: 3000
+```
+
+Reload your virtual machine:
+
+```
+vagrant reload
+```
+
+# Running the rails server
+
+In your virtual machine, run the application server, binding to your local ip address:
+
+```
+bin/rails s -b 0.0.0.0
+```
+
+Now you should be able to see the application running in your browser at url `localhost:3000`! :tada: