Add missing files

Signed-off-by: aradermache <ansgar.radermacher@cea.fr>

build.adoc

+== Build
+
+The build process for P4R is based on maven. For compiling, a target platform and a compilation goal needs to be specified.
+
+For instance
+
+`  mvn install -P 2019-12,product`
+
+will create an RCP product (for Linux, MacOS and Windows-10 based on the 2019-12 target platform.
+
+`  mvn install -P 2020-06,p2`
+
+creates a P4R update-site based on the Eclipse 2020-06 platform.
+
+Besides of the (manual) execution on a (unix-based) machine, the build is executed on the Eclipse continuous integration server, see https://ci.eclipse.org/papyrus/view/Robotics[P4R view].