hg: jdk9/sandbox/jdk: 8167981: Optional: add notes explaining intended use

[chris.hegarty at oracle.com]

Changeset: 533d7278264b
Author:    smarks
Date:      2017-04-20 11:40 -0700
URL:       http://hg.openjdk.java.net/jdk9/sandbox/jdk/rev/533d7278264b

8167981: Optional: add notes explaining intended use
Reviewed-by: martin, psandoz

! src/java.base/share/classes/java/util/Optional.java
! src/java.base/share/classes/java/util/OptionalDouble.java
! src/java.base/share/classes/java/util/OptionalInt.java
! src/java.base/share/classes/java/util/OptionalLong.java