output for missing option, added working program call to readme

Author: roman-la

README.md

@@ -29,8 +29,10 @@ You may use the following parameters when calling the program:
 
 Example call:
 ```
-java -jar XXX.jar -osm 5cc58071facf70001a872bef -measurements
-                  -timerange 2019-05-01T00:00:00.000Z 2019-05-15T00:00:00.000Z -path /rdf.out
+java -jar XXX.jar -osm 5cc58071facf70001a872bef
+                  -measurements
+                  -timerange 2019-05-01T00:00:00.000Z 2019-05-15T00:00:00.000Z
+                  -path file.out
 ```
 
 ### Tests

src/main/java/Main.java

@@ -1,4 +1,5 @@
 import org.apache.commons.cli.CommandLine;
+import org.apache.commons.cli.MissingOptionException;
 import org.apache.commons.cli.ParseException;
 
 import osm.util.OpenSenseMapHandler;
@@ -9,10 +10,18 @@
 public class Main {
     public static void main(String[] args) throws ParseException, IOException {
 
-        CommandLine config = new Config().parseArgs(args);
+        try {
+            CommandLine config = new Config().parseArgs(args);
 
-        if (config.hasOption("osm")) {
-            new OpenSenseMapHandler().handleConfig(config);
+            if (config.hasOption("osm")) {
+                new OpenSenseMapHandler().handleConfig(config);
+            } else {
+                System.out.println("No data source specified.");
+                System.out.println("Please refer to the README.");
+            }
+        } catch (MissingOptionException e) {
+            System.out.println("You are missing the following options: " + e.getMissingOptions());
+            System.out.println("Please refer to the README.");
         }
     }
 }