Packaging Tutorial: minor updates

[adamjstewart]

Minor grammar stuff and line numbers.

I noticed that the example from spack create does not contain a line for the new license(...) directive. Are we not auto-generating those files?

Tomorrow once the docker images are available, I'm going to walk through the entire tutorial one more time myself and add the license stuff.

[adamjstewart]

@tldahlgren just a heads up, I removed many of the emphasize-lines from this tutorial. Specifically, I removed them from all auto-generated output that frequently changes and only kept them for package.py files which we control and configure --help output which will never change. This will make it easier to maintain this in the future. But feel free to add some of these back next time you present this section.