Update instructions regarding debug logging

The debug flag is supposed to be passed through `odbcinst.ini`. Unfortunately, there is some bug in the `.ini` parsing code. If you pass it through `odbc.ini`, it works.

The important flag in odbcinst.ini works (specifiying the library location). I think it may be that some flags are copied from odbc.ini to odbcinst.ini, overwriting certain configurations, but I'm not sure. This fix updates the instructions regarding logging.