add .gitignore

for clean branch switching
init using tunet.lab.mu
add v1.3-rc2
use /latest instead of raw download link
add v1.2 stable apk
Better width for QR code.
Minor changes on iOS description.
Minor change on texts.
Hide QRCode and its Text when width is small.
Allow gh-pages also works for downloading.

see http://mulab.github.io/TUNet/
add nginx config file