Add sample code

[srl295]

This was my thought: (U+2615 is "hot beverage") Encoding:

$ imghash --name CHAI --content-type image/png --base 0x2615 --data chai.png --write out.txt
# hash is YYYYYYYY
# Writing to out.txt:  U+2615 U+DXXXX U+DXXXX
…

Decoding:

$ imghash --decode out.txt
# Found base char U+2615 with hash YYYYYYYY
…