Update PULL_REQUEST_TEMPLATE URL

Author: baijunyao

.github/PULL_REQUEST_TEMPLATE.md

@@ -16,7 +16,7 @@
 
  If you're working on a different localization (not English), or you
  are documenting a feature that will be part of a future release, see
- https://kubernetes.io/docs/contribute/start#choose-which-git-branch-to-use
+ https://kubernetes.io/docs/contribute/new-content/overview/#choose-which-git-branch-to-use
  for advice.
 
 -->