Add info about GIO modules variable to README

[emilmelnikov]

I am using Ubuntu 16.04, and installation instructions from the README didn't work for me.
The script ran without errors, but the following message appeared:

GLib-GIO-Message: Using the 'memory' GSettings backend.  Your settings will not be saved or shared with other applications.

The solution is described in this StackOverflow answer: before running the script, export the GIO_EXTRA_MODULES variable (it is OK to set it only for the current session).

export GIO_EXTRA_MODULES=/usr/lib/x86_64-linux-gnu/gio/modules

On a side note, add an installation one-liner to README:

curl -sL https://raw.githubusercontent.com/arcticicestudio/nord-gnome-terminal/develop/src/nord.sh | bash

[arcticicestudio]

Thanks for your contribution 👍 and sorry for my late reply, currently busy with studying next to my job as dev. I'll take a look at it this weekend. Might be interesting to get to know the version this change has been introduced to GLib/GIO.

Also looks like this will solve #20.