added docs to the repo

docs/_examples/update.asciidoc

@@ -0,0 +1,69 @@
+.Update document title using partial document
+[source,js]
+---------
+client.update({
+  index: 'myindex',
+  type: 'mytype',
+  id: '1',
+  body: {
+    // put the partial document under the `doc` key
+    doc: {
+      title: 'Updated'
+    }
+  }
+}, function (error, response) {
+  // ...
+})
+---------
+
+.Add a tag to document `tags` property using a `script`
+[source,js]
+---------
+client.update({
+  index: 'myindex',
+  type: 'mytype',
+  id: '1',
+  body: {
+    script: 'ctx._source.tags += tag',
+    params: { tag: 'some new tag' }
+  }
+}, function (error, response) {
+  // ...
+});
+---------
+
+.Increment a document counter by 1 or initialize it, when the document does not exist
+[source,js]
+---------
+client.update({
+  index: 'myindex',
+  type: 'mytype',
+  id: '666',
+  body: {
+    script: 'ctx._source.counter += 1',
+    upsert: {
+      counter: 1
+    }
+  }
+}, function (error, response) {
+  // ...
+})
+---------
+
+.Delete a document if it's tagged “to-delete”
+[source,js]
+---------
+client.update({
+  index: 'myindex',
+  type: 'mytype',
+  id: '1',
+  body: {
+    script: 'ctx._source.tags.contains(tag) ? ctx.op = "delete" : ctx.op = "none"',
+    params: {
+      tag: 'to-delete'
+    }
+  }
+}, function (error, response) {
+  // ...
+});
+---------