Minor documentation updates

app/models/concerns/mentionable.rb

@@ -25,7 +25,7 @@ module Mentionable
   # By default this will be the class name and the result of calling
   # `to_reference` on the object.
   def gfm_reference
-    # Convert "MergeRequest" to "merge request"
+    # "MergeRequest" > "merge_request" > "Merge request" > "merge request"
     friendly_name = self.class.to_s.underscore.humanize.downcase
 
     "#{friendly_name} #{to_reference}"

app/models/concerns/referable.rb

@@ -40,7 +40,7 @@ module Referable
     #
     # This must be overridden by the including class.
     #
-    # Returns Regexp
+    # Returns a Regexp
     def reference_pattern
       raise NotImplementedError,
         %Q{#{self} does not implement "reference_pattern"}