README: update readme for UT2
README: update readme for UT2

kalmog/tectonic-installer,squat/tectonic-installer,squat/tectonic-installer,lander2k2/tectonic-installer,kalmog/tectonic-installer,lander2k2/tectonic-installer,kalmog/tectonic-installer,derekhiggins/installer,cpanato/tectonic-installer,squat/tectonic-installer,derekhiggins/installer,lander2k2/tectonic-installer,squat/tectonic-installer,cpanato/tectonic-installer,cpanato/tectonic-installer,cpanato/tectonic-installer,lander2k2/tectonic-installer