net/url: clarify why @ is allowed in userinfo
Add comment to clarify why '@' is allowed in validUserinfo func.
Change-Id: Ia9845bc40fea6c34093434d57bb1be4ddbc70b84
GitHub-Last-Rev:
ce65168ab03afd879ad028de295f6adb7ee1c97d
GitHub-Pull-Request: golang/go#73195
Reviewed-on: https://go-review.googlesource.com/c/go/+/663455
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Damien Neil <dneil@google.com>
Auto-Submit: Damien Neil <dneil@google.com>