[DOCS] Update painless statements with if/else example
Painless supports all of Java's https://docs.oracle.com/javase/tutorial/java/nutsandbolts/flow.html[
control flow statements] except the `switch` statement.
+==== Conditional statements
+
+===== If / Else
+
+[source,painless]
+---------------------------------------------------------
+if (doc[item].size() == 0) {
+ // do something if "item" is missing
+} else {
+ // do something else
+}
+---------------------------------------------------------
+
+==== Loop statements
+
+===== For
+
Painless also supports the `for in` syntax from Groovy:
[source,painless]
