you can use it in any *.md file within Github
it's RELATIVE links so it'll be valid in all forks of your project
the project's root
[root](/../../) (default branch)
the current folder
[current](./) (exept root folder)
a file in the current folder current/readme.md
[current/readme.md](./readme.md)
full path from root
[from root](/doc/readme.md)
another brunch test
[test](/../../tree/test)
open in editor doc/readme.md
[doc/readme.md](/../../edit/master/doc/readme.md)
view history of doc/readme.md
[doc/readme.md](/../../commits/master/doc/readme.md)
delete(!) doc/readme.md
[doc/readme.md](/../../delete/master/doc/readme.md) (it will offer to create a commit to delete file)
blame mode doc/readme.md
[doc/readme.md](/../../blame/master/doc/readme.md)
raw file doc/readme.md
[doc/readme.md](/../../raw/master/doc/readme.md) (you'll be redirected to raw.githubusercontent.com/...)
new file in doc/
[doc/](/../../new/master/doc/)
new file in doc/newSubFolder
[doc/newSubFolder](/../../new/master/doc/newSubFolder)
ask to upload to doc/
[doc/](/../../upload/master/doc/)
find file in specific brunch find
[find](/../../find/test)
instead of master you can specify another branch name /../../upload/new_brunch/doc/, but be carefull - it's not relative!
in issues you may use this links such way: (../upload/master/doc/)
to open in new tab <a href="/../../edit/master/doc/readme.md" target="_blank">tab</a>