add day1 hello world

Author: syntastical

day1/Example.java

@@ -0,0 +1,5 @@
+public class Example {
+    public static void main(String[] args) {
+        System.out.println("Hello world");
+    }
+}

day1/index.md

@@ -6,4 +6,4 @@ https://en.wikipedia.org/wiki/Java_(programming_language)
 ## Where is it used
 1. Server side applications
 2. Android apps
-3. Desktop (GUI)
+3. Desktop (GUI)