HHH-6154 - Add a README for describing build

README

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+Starting with development of version 4.0, Hibernate uses Gradle (http://gradle.org) as its build tool.  This README describes some of the basics developers and contributors new to Gradle need to know to get productive quickly.  Here is a list of resources to obtain more detailed information about Gradle:
+
+* The Gradle User Guide : http://gradle.org/latest/docs/userguide/userguide_single.html
+* Gradle DSL Guide : http://gradle.org/latest/docs/dsl/index.html
+* Additional Hibernate/Gradle information : http://community.jboss.org/wiki/GradleFAQ
+
+Executing Tasks Across All Modules
+----------------------------------
+To execute a task across all modules, simply perform that task from the root directory.  Gradle will visit each
+subproject and execute that task if the subproject defines it.
+
+Executing Tasks In Specific Module
+----------------------------------
+To execute a task in a specific module you can either:
+1. `cd` into that module directory and execute the task
+2. name the "task path".  For example, in order to run the tests for the hibernate-core module from the root directory
+    you could say `gradle hibernate-core:test`
+
+Common Java-module tasks
+------------------------
+* build - Assembles (jars) and tests this project
+* buildDependents - Assembles and tests this project and all projects that depend on it.  So think of running this in hibernnate-entitymanager, Gradle would assemble and test hibernate-entitymanager as well as hibernate-envers (because envers depends on entitymanager)
+* classes - Compiles the main classes
+* testClasses - Compiles the test classes
+* jar - Generates a jar archive with all the compiled classes
+* test - Runs the tests
+* uploadArchives - Think Maven deploy
+* install - Installs the project jar to your local maven cache (aka ~/.m2/repository)
+* eclipse - Generates an Eclipse project
+* idea - Generates an IntelliJ/IDEA project.
+* clean - Cleans the build directory