Add docs

nanoc/lib/mixin/erb.rb

@@ -1,6 +1,15 @@
 # frozen_string_literal: true
 
+##
+# The {Mixin::ERB Mixin::ERB} module provides a method
+# that can render an ERB template
 module Mixin::ERB
+  ##
+  # @param [String] file
+  #  The path to an ERB template
+  # @param [Hash] local_assigns
+  #  Template variables
+  # @return [String]
   def erb(file, local_assigns = {})
     erb = File.binread File.join(dirs.content, "html", file)
     ctx = binding

nanoc/lib/mixin/t.rb

@@ -1,11 +1,25 @@
 # frozen_string_literal: true
 
+##
+# The {Mixin::T Mixin::T} module provides a method that
+# can render user-facing text strings in different
+# locales / languages
 module Mixin::T
+  ##
+  # @param [String] locale
+  #  Locale (eg "en")
+  # @param [String] key
+  #  Translation key (eg "TheNobleQuran")
+  # @param [Hash] local_assigns
+  #  Template variables
+  # @return [String]
   def t(locale, key, local_assigns = {})
     str = [locale, *key.split(".")].inject(tdata) { _1[_2] }
     format(str, local_assigns)
   end
 
+  private
+
   def tdata
     @tdata ||= Ryo.from_json(path: File.join(dirs.content, "json", "t.json"))
   end