Update README to clarify the protocol value in DATABASE_URL
Update README to clarify the protocol value in DATABASE_URL

Resolves #1047
brianmario/mysql2,sodabrew/mysql2,sodabrew/mysql2,kamipo/mysql2,brianmario/mysql2,sodabrew/mysql2,kamipo/mysql2,kamipo/mysql2,kamipo/mysql2,jeremy/mysql2,jeremy/mysql2,brianmario/mysql2,jeremy/mysql2