Guidelines for suggested usage of CLI packages

[parlough]

Help developers decide what method of using their published CLI package they should use/recommend.

Rough sketch of potential flow:

1. If closely tied to package also used as normal dependency, no extra dependency, just dart run package:command.
2. If a separate package that is tied to other dependencies a package might have or each contributor should have the same version of, add as dev dependency, then dart run package:command.
3. (Doesn't exist yet) If unrelated to dependencies of a package or used outside a package, one-off global run command.
4. (Discouraged) If desired to have a binstub to use without dart run or dart pub global run, then dart pub global activate.