[5507] Updated readme for new branches

readme.textile

@@ -19,6 +19,25 @@ It can be easily launched on the console using @javaws  http://ifedorenko.github
 
 * No Eclipse RCP product is built, as we assume that the core product is distributed using the Elexis 3 core.
 
+h2. Building
+
+You need Java 1.8+. Maven >= 3.3. Then you should be able to generate a p2 update site using the following calls:
+
+@git clone https://github.com/elexis/elexis-3-base@
+@cd elexis-3-base@
+@mvn -V -Dtycho.localArtifacts=ignore -Dmaven.test.skip=true clean verify@
+
+Remarks:
+* -V: emits version of Java, Maven, GUI-Toolkit, Architecture. Handy when you ask a problem
+* clean: Build everything from scratch
+* verify: Compile, test and build a P2-site including products. But does NOT install maven artefacts
+* -Dtycho.localArtifacts=ignore: Do not use any locally built maven artefacts
+* -Dmaven.test.skip=true: Skip unit tests (Use it only if you want to speed up the build)
+* Jenkins-CI job copIES the generated the *p2site\target\repository to a subdirectory reachable under  http://download.elexis.info/elexis/<branch-name>/p2/elexis-3-base
+* Add `-Dmaven.test.skip=true` if you want to skip running the unit tests.
+* -Drepo_variant=release as starting with branch 3.3 we begin to use the P2 named like http://download.elexis.info/elexis/<branch-name>/ and use branch names likes 3.3, 3.4
+
+After the build use Help..Add New Software add a new 'local' p2 site pointing at the generated ch.elexis.base.p2site\target\repository directory and install the desired plugins
 
 h2. TODO