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.