Update for installFeature doc

[cherylking]

This would affect LMP also.

The documentation for installFeature does not make it clear that when installing a user feature on Open Liberty, you must provide a features BOM file and include it in the build.gradle as a dependency. The doc doesn't even mention user features. Some examples would be good.

Need to check if specifying a local file path to the ESA file in the build.gradle works or not for user features. If not, flag that config as invalid.

The user that reported problems with this process was Jack Dunning.