fix/update of "Supported C64 Cartridge Types"

[xela74]

Dear Gideon,
I just noticed that "Supported C64 Cartridge Types" (table in howto/cartridges.rst) incorrectly states that Magic Formel (14) is supported, while it is not (CART_NOT_IMPL in software/io/c64/c64_crt.cc).
Plus the newly added support for Blackbox V9 (71) should probably be marked as such, too.

Cheers and thanks for your work,
Alex

[GideonZ]

I'd gladly accept a merge request / pull request. ;-)

[xela74]

Just added a pull request. (Forgot to reference the issue, sorry.)

[mrdudz]

Stumbled about this when updating my table at https://rr.pokefinder.org/wiki/CRT_ID ...

https://1541u-documentation.readthedocs.io/en/latest/howto/cartridges.html is still wrong/incomplete

Also: CRT IDs 22-31 are missing in that table

[GideonZ]

@mrdudz I'd gladly accept a merge request / pull request. ;-)