Tweak AD::Http::FilterParameters code example [ci-skip]

Prior to this commit, the format of the code example confused the syntax
highlighter.  This commit formats each explanation as a code comment,
and tweaks their wording for clarity.

actionpack/lib/action_dispatch/http/filter_parameters.rb

@@ -12,25 +12,25 @@ module Http
     # sub-hashes are passed to it, where the value or the key can be replaced using
     # <tt>String#replace</tt> or similar methods.
     #
+    #   # Replaces values with "[FILTERED]" for keys that match /password/i.
     #   env["action_dispatch.parameter_filter"] = [:password]
-    #   => replaces the value to all keys matching /password/i with "[FILTERED]"
     #
+    #   # Replaces values with "[FILTERED]" for keys that match /foo|bar/i.
     #   env["action_dispatch.parameter_filter"] = [:foo, "bar"]
-    #   => replaces the value to all keys matching /foo|bar/i with "[FILTERED]"
     #
-    #   env["action_dispatch.parameter_filter"] = [ /\Apin\z/i, /\Apin_/i ]
-    #   => replaces the value for the exact (case-insensitive) key 'pin' and all
-    #   (case-insensitive) keys beginning with 'pin_', with "[FILTERED]"
-    #   Does not match keys with 'pin' as a substring, such as 'shipping_id'.
+    #   # Replaces values for the exact key "pin" and for keys that begin with
+    #   # "pin_". Does not match keys that otherwise include "pin" as a
+    #   # substring, such as "shipping_id".
+    #   env["action_dispatch.parameter_filter"] = [ /\Apin\z/, /\Apin_/ ]
     #
+    #   # Replaces the value for :code in `{ credit_card: { code: "xxxx" } }`.
+    #   # Does not change `{ file: { code: "xxxx" } }`.
     #   env["action_dispatch.parameter_filter"] = [ "credit_card.code" ]
-    #   => replaces { credit_card: {code: "xxxx"} } with "[FILTERED]", does not
-    #   change { file: { code: "xxxx"} }
     #
+    #   # Reverses values for keys that match /secret/i.
     #   env["action_dispatch.parameter_filter"] = -> (k, v) do
     #     v.reverse! if k.match?(/secret/i)
     #   end
-    #   => reverses the value to all keys matching /secret/i
     module FilterParameters
       ENV_MATCH = [/RAW_POST_DATA/, "rack.request.form_vars"] # :nodoc:
       NULL_PARAM_FILTER = ActiveSupport::ParameterFilter.new # :nodoc: