You could always make a table to store information, notes and remarks on your Database.
And for the notes:
Someone else just asked a similar question.
If you have a Dashboard style layout that opens erytime you open the file you could put your portal there.
At least during development.
In the relationship dialogue you can make text notes by cliking the "A" symbol in the bottom. Then you can drag a box in between your tables and make notes like that.
When you create fields you can also make comments in the box below.
On the top it says Options / Comments - Click to toggle. So you can see your comments.
In your scripts you can also add comments.