feat: count game data apart from BIOS files

The installer knew BIOS files from game data and no count showed it.
The plan, the line menu and the result count them apart for a list that
marks game data, the plan gets a game data row and the menu a g key,
each toggling it in one press, and one sentence says what game data is.

wiki/first-install.md

@@ -92,6 +92,9 @@ The next screen counts missing files and free space.
 Press Enter on **Install**. **Choose systems** keeps the consoles you
 play.
 
+**Game data** is what a game reads, of no use to other cores. The count
+shows it apart, and its row leaves it out.
+
 **Old card?** In a card reader, choose **Copy the BIOS files from your old
 card or a folder**, then the card.
 
@@ -166,7 +169,8 @@ You cannot write there. Do what the message says.
 
 ### The card is full
 
-Nothing was written. Free some space, or choose another folder.
+Nothing was written. Free some space on the card. On a computer, you can
+also choose another folder.
 
 ### The game still does not start