RFR: 8181825: Add tool and services information to module summary

[Mandy Chung]

> On Jun 8, 2017, at 5:25 PM, Jonathan Gibbons <jonathan.gibbons at oracle.com> wrote:
> 
> Please review minor doc updates to langtools modules to add info
> about tools and services.
> 
> In addition, a previously missing package-info is provided for
> com.sun.tools.javac.
> 
> This is the langtools equivalent of JDK-8181639.
> https://bugs.openjdk.java.net/browse/JDK-8181639
> http://mail.openjdk.java.net/pipermail/core-libs-dev/2017-June/048132.html
> 
> JBS: https://bugs.openjdk.java.net/browse/JDK-8181825
> Webrev: http://cr.openjdk.java.net/~jjg/8181825/webrev.00


You can consider s/just exists/only exists/ suggested by Paul in 
a similiar statement in the jdk module:

  <em>javah</em> just exists as a command line tool,
  <em>jdeprscan</em> just exists as a command line tool,

Otherwise looks good.

Mandy