mention golang implementation of djot parser

[sivukhin]

Didn't find any golang parsers for Djot - so I decided to write my own version of it: godjot

The implementation is a bit bumpy in some places but it passes all examples from the doc and I started to write my own documents using this parser (as a version of dogfooding)

So, I decided to give it a try and add this implementation on the official web site.

[jgm]

You can also mention it at https://github.com/jgm/djot/discussions/265

[3052]

Need to update readme