Using features vs adding dependencies and config changes

[burtbeckwith]

Many of the guides instruct the user to create an app with no features and then add dependencies and make config changes, but often these changes are the same as those made by adding a feature. Adding features when creating the app is better for users creating new apps, but explaining the changes in the guide is better for users wanting to add the guide's functionality to existing apps. We added the diffLink macro to help bridge the two, but it's not sufficient.

One thing that would help is to change the look of the note that's added by the diffLink macro - currently it's easy to miss and may not be clear enough. But it would be good to add more information about creating vs updating, and this should be automated as much as possible. We should be able to use (and possibly add) functionality in starter to determine the changes and use that to generate more explicit upgrade instructions in the output of the diffLink macro.