@broc.seib has a sophisticated answer, I just want to point out that instead of pressing y
to get the permanent link, github now has a very simple UI that helps you to achieve it
Select line by clicking on the line number or select multiple lines by downholding shift
(same as how you select multiple folders in file explorer)
on the right hand corner of the first line you selected, expand ...
and click copy permalink
https://github.com/python/cpython/blob/c82b7f332aff606af6c9c163da75f1e86514125e/Doc/Makefile#L1-L4