Update install documentation for db_password_algorithm

I just installed for the first time FileZ, and I had trouble configuring the db_password_algorithm value:
I first tried with `password=SHA1(CONCAT(salt_column, :password))`, then when I checked the db schema `password=SHA1(CONCAT(salt, :password))`, and finally after checking the code in Database.php I understood I needed `SHA1(CONCAT(salt, :password))`.

In the commits I kept `salt_column` because the other examples are also meta and not literal.