docs: document byte order in parse() and stringify(). fixes #503

[broofa]

No description provided.

[ctavan]

Nice!

Should we mention though that this is the byte order recommended by the RFC but incompatible with they byte order produced by https://docs.microsoft.com/en-us/dotnet/api/system.guid ?

My suspicion is that if anybody runs into problems here, then .NET users where this is the default representation, so I think the note is mostly here to spare them some WTF-moments.

As a side note: Python offers both representations: https://docs.python.org/3/library/uuid.html UUID.bytes and UUID.bytes_le but from the naming it seems like they are treating big endian notation as the default as well.

[broofa]

Should we mention though that this is the byte order recommended by the RFC

Let's not. Between the note and the examples, it's clear what we're doing. I don't think we need to go into the "why" behind it.