Update README: build instruction

Author: ilya-g

README.md

@@ -8,4 +8,8 @@ To initialize submodules, use the following commands:
     git submodule init
     git submodule update
 
-Prototype implementation is based on [pcollections](http://pcollections.org/). Copyright 2015 The pcollections Authors.
+Then you can build artifacts with:
+
+    mvn install
+
+Prototype implementation is based on [pcollections](http://pcollections.org/) (Copyright 2015 The pcollections Authors.)