Teach Zeitwerk that REST is the class name, not Rest

Also add a comment about the inflector settings.

NameError: uninitialized constant InitialStateSerializer::REST
Did you mean?  Rest
/vagrant/app/serializers/initial_state_serializer.rb:7:in `<class:InitialStateSerializer>'
/vagrant/app/serializers/initial_state_serializer.rb:3:in `<main>'

config/initializers/inflections.rb

@@ -10,7 +10,27 @@
 #   inflect.uncountable %w( fish sheep )
 # end
 
-# : TODO : WTF IS THIS?
+
+
+# When converting a file path to a constant name and vice versa, Rails uses inflections to know
+# what to do. It uses the `humanize` method to convert a path to a constant, and it uses
+# `underscore` to convert a constant to a path.
+#
+# The inflections below are ones that do not follow the typical convention of underscore/humanize.
+# Referring to it as an "acronym" is the easiest way to tell it, "this constant should just be
+# downcased to become a path".
+#
+# BEFORE:
+# 'StatsD'.underscore
+# => "stats_d"
+# 'statsd'.humanize
+# => "Statsd"
+#
+# AFTER: (inflect.acronym 'StatsD')
+# 'StatsD'.underscore
+# => "statsd"
+# 'statsd'.humanize
+# => "StatsD"
 ActiveSupport::Inflector.inflections(:en) do |inflect|
   inflect.acronym 'StatsD'
   inflect.acronym 'OEmbed'
@@ -19,4 +39,5 @@ ActiveSupport::Inflector.inflections(:en) do |inflect|
   inflect.acronym 'PubSubHubbub'
   inflect.acronym 'ActivityStreams'
   inflect.acronym 'JsonLd'
+  inflect.acronym 'REST'
 end