RFR: 8023433 : (xs) Improve "make help"

[Tim Bell]

Hi Mike:

> Another tiny changeset with updates to the make help target. This change publicizes the "docs" target and updates the list of components for component specific targets.
>
> http://cr.openjdk.java.net/~mduigou/JDK-8023433/0/webrev/
>
> This change would be integrated via the TL repo as I am not build project committer.

Looks good to me.

noreg-doc... I won't ask you to run the JCK :-)

Tim