To install this indicator applet:

Press Ctrl+Alt+T on keyboard to open the terminal. When it opens, choose one method from below and run the commands one by one:

Compile from source (github.com):

sudo apt-get install build-essential libgtop2-dev libgtk-3-dev libappindicator3-dev git-core

git clone git://github.com/mgedmin/indicator-netspeed.git

cd indicator-netspeed

make

sudo make install

Once installed, start the applet via:

indicator-netspeed &

You need to manually add this applet into Startup Applications (open it from Unity Dash).