Add "remove a tag" script logic as an example

docs/reference/docs/update.asciidoc

@@ -47,7 +47,7 @@ POST test/_doc/1/_update
 // TEST[continued]
 
 We can add a tag to the list of tags (note, if the tag exists, it
-will still add it, since its a list):
+will still add it, since it's a list):
 
 [source,js]
 --------------------------------------------------
@@ -65,6 +65,24 @@ POST test/_doc/1/_update
 // CONSOLE
 // TEST[continued]
 
+We can remove a tag from the list of tags. Note that the Painless function to `remove` a tag takes as its parameter the array index of the element you wish to remove, so you need a bit more logic to locate it while avoiding a runtime error. Note that if the tag was present more than once in the list, this will remove only one occurrence of it:
+
+[source,js]
+--------------------------------------------------
+POST test/_doc/1/_update
+{
+    "script" : {
+        "source": "if (ctx._source.tags.contains(params.tag)) { ctx._source.tags.remove(ctx._source.tags.indexOf(params.tag)) }",
+        "lang": "painless",
+        "params" : {
+            "tag" : "blue"
+        }
+    }
+}
+--------------------------------------------------
+// CONSOLE
+// TEST[continued]
+
 In addition to `_source`, the following variables are available through
 the `ctx` map: `_index`, `_type`, `_id`, `_version`, `_routing`
 and `_now` (the current timestamp).