Add information about VRAM address space layout

[joolin1]

I suggest that information about the default location of the text layer and the character set is added to the table "VRAM address space layout". You can make a VPEEK, you get bits 16-9 of the address, and then you can calculate this yourself. But why not write it in the documentation directly? This is what I miss:

$1B000 - $1EBFF Default location of screen memory for text layer (layer 1)
$1F000 - $1F7FF Default location of character set

[mooinglemur]

This information is already given here https://github.com/X16Community/x16-docs/blob/master/X16%20Reference%20-%2008%20-%20Video%20Programming.md