Tools/ros: add license info

Tools/ros/vagrant/docker-host-base/Vagrantfile

@@ -9,6 +9,8 @@
 # After build, do "vagrant package --base docker-host-base" to package,
 # and import as box: "vagrant box add --name uaventure/docker-host-base package.box"
 #
+# License: according to LICENSE.md in the root directory of the PX4 Firmware repository
+
 Vagrant.configure(2) do |config|
   config.vm.box = "ubuntu/trusty64"
 
@@ -19,7 +21,7 @@ Vagrant.configure(2) do |config|
     vb.gui = true
     vb.memory = "1024"
   end
-  
+
   config.vm.provision "file", source: "config/docker-default", destination: "/home/vagrant/docker-default"
   config.vm.provision "file", source: "config/xsessionrc", destination: "/home/vagrant/.xsessionrc"