doc: listed the apt commands more clearly

For Ubuntu/etc: Added apt-get update item. Also made the nightly build
PPA a bit less obvious than the stable one (which I'd imagine most
people will want). Fixed some formatting of commands in item 3.
Added pip install for pyinstaller
doc: No need to run python pyinstaller.py

Once pip has installed it it just gets added to the path
doc: No longer packaging *all* files in source dir

This is somewhat subjective (and perhaps both options should be given)
but generally I don't want to package every single file in my source
project to go into the output folder. I've added an example which just
picks kv and png files - I think this is better than the current example
(using Tree) because it's easier to cut mine down to add all files than
it is to expand the existing example to cherry-pick.