docs: Fix link to visual testing
In !1219 (comment 310611245) it was pointed out that our README linked to a dead end when looking for how to update our visual test snapshots.
This fixes that link.
Edited by Mark Florian
In !1219 (comment 310611245) it was pointed out that our README linked to a dead end when looking for how to update our visual test snapshots.
This fixes that link.