Update README.md

Added the security shield from Hakiri.
Merge pull request #3216 from vasinov/master

Update README.md
use authentication_keys in flash message, instead of static ‘username’ (fix #3201)
Merge pull request #3218 from timoschilling/fix_3201

use authentication_keys in flash message (fix #3201)
use auth keys from scope instead of global config
use I18n "support.array.words_connector" as connector
code cleanup FailureApp
fix argument bug

when `is_navigational_format?` returns false, Exception will be throw: 
ArgumentError (Nil location provided. Can't build URI.)
Merge pull request #3229 from yandy/patch-1

fix path bug
Merge pull request #3221 from timoschilling/auth_keys_text

fix and optimice authentication_keys