Add Wordsmith::Inflection customization docs

Wordsmith has somewhat opinionated defaults that can be hard to customize, as detailed in this issue:
https://github.com/luckyframework/wordsmith/issues/17

My guidance to a new Lucky user was to do something like this when a bunch of overrides/customization are needed, effectively clearing out all defaults and building back up from scratch with what will work for your app:

# config/inflections.cr

module Wordsmith
  Inflector.inflections.clear

  Inflector.inflections.plural(/$/, "s")
  Inflector.inflections.plural(/s$/i, "s")

  # etc, etc, etc
end

We should probably include some kind of note or reference to the Wordsmith docs in the guides around the pluralization text helper section.

Start with the Lucky guides section covering the pluralization text helper and review the linked Wordsmith issue about inflection defaults. Add a note or reference to Wordsmith's inflection customization guidance, including the documented approach for clearing and rebuilding defaults, then verify the guide renders correctly.