Update documentation with custom layer support for bootable JAR

In XP 2.0.0, including custom layers in a bootable JAR was not supported.  

After this capability is tested, we will need to implement the following updates:

• A new section must be added to the bootable JAR section in the XP user guide describing how to implement custom layers in the bootable JAR.
• In the capability trimming content, we must add a link to the new custom layer section in the bootable JAR content. Some text revisions may also be necessary