What's the location of "database.config" in Mongify?

I am using Mongify to convert my SQL Server database to Mongo database. I followed the documentation and got lost when referencing a file database.config

.

I tried to create it and dump it:

C:\Ruby21-x64\lib\ruby\gems\2.1.0\gems\mongify-1.2.4

      

        
        
        
      

    

But it didn't work when I ran:

mongify check database.config

      

        
        
        
      

    

Where should I deliver database.config

?