Add info keyboard layout

[Luis46coco]

 ```

CoCo 3 Keyboard +-----------------------------------------------------------------------------+ | [1!][2"][3#][4$][5%][6&][7'][8(][9)][0][:*][_:] [esc/Break] | | [Alt][Qq][Ww][Ee][Rr][Tt][Yy][Uu][Ii][Oo][Pp][ @ ][Clear] [ Up-A ] | | [Cntrl][Aa][Ss][Dd][Ff][Gg][Hh][Jj][Kk][Ll][;+][Enter] [Left-A][Right-A] | | [Shift][Zz][Xx][Cc][Vv][Bb][Nn][Mm][,<][.>][/?][RShift] [ Down-A ] | | [ Space ] [ F1 ][ F2 ] | +-----------------------------------------------------------------------------+

    Rows and columns
    +-----------------------------------------------------*
    |      0-----1-----2-----3-----4-----5-----6-----7    |
|  0-[ @ ]-[ A ]-[ B ]-[ C ]-[ D ]-[ E ]-[ F ]-[ G ]  |
|  1-[ H ]-[ I ]-[ J ]-[ K ]-[ L ]-[ M ]-[ N ]-[ O ]  |
|  2-[ P ]-[ Q ]-[ R ]-[ S ]-[ T ]-[ U ]-[ V ]-[ W ]  |
|  3-[ X ]-[ Y ]-[ Z ]-[UpA]-[DnA]-[LfA]-[RgA]-[spc]  |
|  4-[ 0 ]-[1 !]-[2 "]-[3 #]-[4 $]-[5 %]-[6 &]-[7 ']  |
|  5-[8 (]-[9 )]-[: *]-[; +]-[, <]-[_ =]-[. >]-[/ ?]  |
|  6-[ENT]-[CLR]-[BRK]-[F1 ]-[F2 ]-[F3 ]-[F4 ]-[Shf]  |
    +-----------------------------------------------------+

    TODO: explain and add link or reference to CoCo 'scan codes' for each key

[BGPierce]

I see no reason to include a scancode chart. Such charts exist in several Color Computer books and documents. VCC is just an emulation of a machine, not a programming reference. VCC's documentation is to explain how to run the machine, not how to program it.