basic.md: packet data tables mix up ASCII chars and decimal values

[pyropeter]

I found the mix of ASCII characters and decimal byte values very confusing, even though I know how a domain name is encoded.

e.g.:

*                                    1  1  1  1  1  1  *
*      0  1  2  3  4  5  6  7  8  9  0  1  2  3  4  5  *
*    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ *
*    |           3           |             w         | *
*    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ *
*    |           w           |             w         | *

is it a decimal 3 or the ascii character 3?

P.S.: Thanks for doing this! ❤️