doc: fix links to runtime Environment Variables
Change-Id: I9e8ecc5e4f4cba0b09008b2b0d9d3f8842687ec3
GitHub-Last-Rev:
e0ddaaed3875761a1ff3692af49c0ec2622a5e20
GitHub-Pull-Request: golang/go#74180
Reviewed-on: https://go-review.googlesource.com/c/go/+/681516
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Junyang Shao <shaojunyang@google.com>
Reviewed-by: Sean Liao <sean@liao.dev>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Sean Liao <sean@liao.dev>