Update usage

README.md

 # km3mon
 
 Monitoring facility for the KM3NeT neutrino detector.
+
+## Usage
+
+Check out the configure options with
+    ./configure --help
+
+then configure the ``Makefile`` with
+    ./configure
+
+and run
+    make start
+
+to start the monitoring. If you want to stop it:
+    make stop
+
+easy.