README.md: add three more questions to the FAQ

The new questions are:
* Is there a public Maven repository with release builds?
* Where can I find a working example of how to configure the NAR plugin?
* How can I test the latest SNAPSHOTs?

These are in response to recent activity on the public mailing list.
README.md: use pluginRepository tags

I inadvertently propagated a mistake from the mailing list. The tag
needs to be "pluginRepository" not "repository" or else Maven will not
use the repository to for resolution of plugin artifacts.
Add a buildhive-settings.xml for use with the BuildHive job

We have a BuildHive job to provide continuous integration and testing here:

	https://buildhive.cloudbees.com/job/maven-nar/job/maven-nar-plugin/

Unfortunately, the cpptasks-parallel artifact is not deployed to where
BuildHive looks for it, and therefore the BuildHive job only succeeds
sporadically (whenever the cpptasks-parallel job has been built
successfully, for a limited amount of time).

BuildHive allows specifying an alternate settings.xml file for such
cases. Since we deployed cpptasks-parallel to the ImageJ Maven
repository, let's have such a file so that our BuildHive job fails only
when the code has a problem.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Merge pull request #28 from scijava/imagej-settings

Add a settings.xml for use with the BuildHive job
Fix it0016-layout

This developer forgot that change in e95475ac(Completely rename the
plugin to 'nar-maven-plugin').

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Merge pull request #30 from scijava/it16-plugin-name-fix

Fix it0016-layout