[PRG] document added charsets (#55)

X16 Reference - 04 - KERNAL.md

@@ -1317,12 +1317,15 @@ Registers affected: .A, .X, .Y
 
 **Description:** A call to this routine uploads a character set to the video hardware and activates it. The value of .A decides what charset to upload:
 
-| Value | Description          |
-|-------|----------------------|
-| 0     | use pointer in .X/.Y |
-| 1     | ISO                  |
-| 2     | PET upper/graph      |
-| 3     | PET upper/lower      |
+| Value | Description                 |
+|-------|-----------------------------|
+| 0     | use pointer in .X/.Y        |
+| 1     | ISO                         |
+| 2     | PET upper/graph             |
+| 3     | PET upper/lower             |
+| 4     | PET upper/graph (thin)      |
+| 5     | PET upper/lower (thin)      |
+| 6     | ISO (thin)                  |
 
 If .A is zero, .X (lo) and .Y (hi) contain a pointer to a 2 KB RAM area that gets uploaded as the new 8x8 character set. The data has to consist of 256 characters of 8 bytes each, top to bottom, with the MSB on the left and set bits representing the foreground color.