Add missing ABOUT file for Base32 snippet

See https://github.com/nexB/vulnerablecode/blob/d3f314dce082e1b70350019137687a1d214b19f2/vulnerabilities/utils.py#L382
It may be best extracted in its own file so it can be used elsewhere too.

While at it it would be useful to consider reverting to use the standard base32 from Python which is an RFC 4648 Base32 standard .... https://en.wikipedia.org/wiki/Base32#RFC_4648_Base32_alphabet as a standard e.g. "_b32alphabet = b'ABCDEFGHIJKLMNOPQRSTUVWXYZ234567"
At least if we use it to encode paths, then a standard is the best option.