Improve casing in encryption guide headings
Improve casing in encryption guide headings

Update the guide to use the casing as defined in the contribution guide.
https://guides.rubyonrails.org/ruby_on_rails_guides_guidelines.html#headings
[ci-skip]

Co-authored-by: Jonathan Hefner <3692bfa45759a67d83aedf0045f6cb635a966abf@hefner.pro>

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