README update and minor setup-release.py change

**README error**

if you just run `pyrcc4 icons.qrc -o gui/icons_rc.py` as stated in the README, you get the following error when starting Electrum
```
Error: Could not import icons_rc.py, please generate it with: 'pyrcc4 icons.qrc -o gui/qt/icons_rc.py'
```

**setup-release.py**

ports do not necessarily install `qt_menu.nib` in `/opt/local/lib/Resources/`
it could be anywhere under `/opt/local`, changed code to search /opt/local, if necessary