Add ROS installation requirements to the installation instructions.

docs/src/main/sphinx/installing.rst

 Installing rosjava_core
 =======================
 
-rosjava_core should be installed using rosws. See the `rosws tutorial`_ for more information.
+These instructions assume that you have already installed ROS on your system.
+See :roswiki:`ROS/Installation` if you need help installing ROS.
 
-.. _rosws tutorial: http://www.ros.org/doc/api/rosinstall/html/rosws_tutorial.html
+When choosing a release to install, please consider that:
+
+* The *oldest* ROS release that rosjava has been tested with is: **Electric**
+* The *newest* ROS release that rosjava has been tested with is: **Electric**
+
+These instructions also assume you are using Ubuntu. However, the differences
+between platforms should be minimal.
 
-The following instructions configure rosjava_core for electric on Ubuntu.
+The recommend installation procedure is to use rosws. See the `rosws tutorial`_
+for more information if you find the following quick start instructions to be
+insufficient.
+
+.. _rosws tutorial: http://www.ros.org/doc/api/rosinstall/html/rosws_tutorial.html
 
 #. sudo apt-get install easy_install
 #. easy_install --prefix ~/.local -U rosintall
@@ -14,5 +25,6 @@ The following instructions configure rosjava_core for electric on Ubuntu.
 #. rosws merge /opt/ros/electric/.rosinstall
 #. rosws merge http://rosjava.googlecode.com/hg/.rosinstall
 
-Don't forget to source the appropriate new setup shell script.
+.. note:: The rosws tool will remind you as well, but don't forget to source
+  the appropriate, newly generated setup script.