Adds security note to param logging

[danielpowell4]

What does this PR do?

Updates the readme to include a note about filtering passwords and other sensitive information.

Commit message:

Adds security note to param logging

Good for this to be top of mind so no one traverses as such:

config.lograge.custom_payload do |controller|
  exceptions = %w(controller action format authenticity_token)
  {
    params: controller.request.params.except(*exceptions), # request.params is DANGEROUS
  }
end

request.filtered_parameters is at least a bit safer as noted in #28

[joshkinabrew]

For future travelers... here's an example of how this would work (running Rails 6.1):

  config.lograge.custom_payload do |controller|
    param_filter = ActiveSupport::ParameterFilter.new(Rails.application.config.filter_parameters)
    { params: param_filter.filter(controller.request.params) }
  end

This way you can still keep the settings in Rails.application.config.filter_paramters in config/initializers/filter_parameter_logging.rb

mentioning #28 so it shows in the comments at the bottom (where I came from)

[iloveitaly]

@joshkinabrew could you create a separate PR to include that example in the readme? I think that would be a helpful example to have!