#1459 - create paper_trail.rb initializer that disables versioning on touch events by default.

[ngobin]

rails generate paper_trail:install creates a paper_trail.rb initializer file that disables versioning on touch events by default. The initializer file also has examples for the other significant global config settings mentioned in the readme.

install_generator.rb already contained old comments about creating an initializer file, however the initializer generation was removed when association tracking was split off in 2018 (Commit 1d42d0d).

Thank you for your contribution!
Check the following boxes:

• Wrote [good commit messages][1].
• Feature branch is up-to-date with master (if not - rebase it).
• Squashed related commits together.
• Added tests.
• Added an entry to the Changelog if the new
  code introduces user-observable changes.
• The PR relates to only one subject with a clear title
  and description in grammatically correct, complete sentences.