Update README.md (#66)

* Update README.md

* Adding intro line

README.md

@@ -1,16 +1,31 @@
 # k4RecCalorimeter - Key4hep Framework Components for Calorimeter Reconstruction
 
-
-## Dependencies
-
-All dependencies can be set up from the Key4hep nightly builds (on lxplus / Centos7 machines with CVMFS)
+The components are available from the Key4hep stack on machines with CVMFS.
 
 ```
 source /cvmfs/sw-nightlies.hsf.org/key4hep/setup.sh
 ```
 
+## Dependencies
+
+* Gaudi
+* ROOT
 * EDM4HEP
 * k4FWCore
 * DD4hep
 * k4geo
 
+
+## Building
+
+After fetching the repository, do
+```
+source /cvmfs/sw.hsf.org/key4hep/setup.sh
+mkdir build install
+cd build
+cmake -DCMAKE_INSTALL_PREFIX=install ..
+make -j4
+make install
+cd ..
+k4_local_repo  # will update all necessary environment variables
+```