Add issue templates

[PgBiel]

Should help people use the appropriate labels and formats for issues.

[laurmaedje]

We could also add a link to Typst's issue choice picker to encourage people to report bibliography bugs here directly. Otherwise the templates will often not be used.

[PgBiel]

Good idea , though I think both ideas complement each other (the hayagriva link would lead to an issue template made for bib bugs, which adds the bug label and stuff)

Edit: I misread your "also" as "instead", sorry :)

Yep, let's do it!