A very simple "make install" for linux

For better integration in my system, this installs Zed somewhere safe, plus a wrapper shell script and .desktop file so I can launch it more easily.

My OSX VM is broken at the moment so I'm not 100% sure I didn't break anything, but say 98%.

Bonus: just typing "make" will now build the app for your native platform. (Should I update the README?)
Not everybody has node.js installed, and if they do, in 90% of the cases it won't be called `nodejs` but `node` (I think only the new Ubuntu calls the binary nodejs). Perhaps this can be rewritten to use perl or something?