[OpenSER-Docs] PDT module doc

[Johansson Olle E]

The PDT module docs are not very clear that it keeps the list in- 
memory and loads at reload. It's only by checking the MI commands you  
figure this out. I suggest that this be improved. Also, the database  
structure is not where the doc says it is any more.

And maybe Ramona wants to change company name and e-mail address while  
looking at this :-)

Greetings from northern Portugal!

/Olle