Create seed data for users and admin for development env

[onurozgurozkan]

• Check that Rails.env == development
• 1 admin [email protected] 1234123
• 3 user [email protected] 12341234, [email protected] 12341234, [email protected] 12341234
• Add users and admin email and password to README.md

NOTE: All passwords are 12341234

[marjinal1st]

By the way, we shouldn't forget that we will need to update seeds.rb when we add required fields for users. Otherwise, we won't be able to create default users from seeds.rb.