(I need it working for any forks)
So it looks like the only way it\'s to provide a link to
After some research I've found this solution:
[the real relative root of any fork](/../../)
It always points to the default branch. For me it's Ok, so it's up to you
PS
With such a trick you can also access the following abilities:
[test](/../../tree/test) - link to another branch
[doc/readme.md](/../../edit/master/doc/readme.md) - open in editor
[doc/readme.md](/../../delete/master/doc/readme.md) - ask to delete file
[doc/readme.md](/../../commits/master/doc/readme.md) - history
[doc/readme.md](/../../blame/master/doc/readme.md) - blame mode
[doc/readme.md](/../../raw/master/doc/readme.md) - raw mode (will redirect)
[doc/](/../../new/master/doc/) - ask to create new file
[doc/](/../../upload/master/doc/) - ask to upload file
[find](/../../find/test) - find file