Add some documentation for `localHostname`
Add some documentation for `localHostname`

Change-Id: Ib56a233731450ff1085bf66fe672a94cf865bd69
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/217026
Reviewed-by: Alexander Aprelev <dfb74c35a357c2059971a4bf7fe26b6a7c18085d@google.com>
Commit-Queue: Brian Quinlan <2ba0baab12cbdc73959f1aa8397b55b4d7de9371@google.com>

dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk