[Feature] Add version of witgen to generated comment

[willemneal]

Currently this comment is at the top of the final generated wit file. This line could also indicate which version of witgen was used to produce the file.

// This is a generated file by witgen (https://github.com/bnjjj/witgen), please do not edit yourself, you can generate a new one thanks to cargo witgen generate command

[bnjjj]

Yes indeed ! It's a good idea. Will do it :)

[willemneal]

fixed by #10