Thank you very much for a swift reply! 
defaults write com.apple.Finder AppleShowAllFiles TRUE 
killall Finder 
That worked, and I can open and edit .htaccess 
I uncommented the rewrites and saved, then installed. 
but no. 
after installation, there is still no /processwire directory . The installer shows green everywhere. 
Just making sure, where should I put the ProcessWire-master folder containing the installation? I have it in the root of my "apache2/htdocs" that I use for development. Should it go somewhere else, like in the apps folder where phpmyadmin resides or something? 
...getting closer, but not quite there yet.