Fix docs about definition file paths

[r7kamura]

The current implementation seems to load all definition files that match the following pattern in this order:

1. factories.rb
2. factories/**/*.rb
3. test/factories.rb
4. test/factories/**/*.rb
5. spec/factories.rb
6. spec/factories/**/*.rb

factory_bot/lib/factory_bot/find_definitions.rb

Lines 10 to 24 in 053ef4a

	self.definition_file_paths = %w[factories test/factories spec/factories]
	def self.find_definitions
	absolute_definition_file_paths = definition_file_paths.map { |path| File.expand_path(path) }
	absolute_definition_file_paths.uniq.each do |path|
	load("#{path}.rb") if File.exist?("#{path}.rb")
	if File.directory? path
	Dir[File.join(path, "**", "*.rb")].sort.each do |file|
	load file
	end
	end
	end
	end

There are several documents that mention definition file paths, but none of them are consistent with the current implementation. So I propose to first eliminate the gap between the documentation and the implementation in this pull request.

I would also be interested to know if this implementation is intentional or not, as it is important to know which files should be ideally scanned by rubocop-factory_bot.