Add minimum documentation

Author: tobias-o

src/elastic/src/client/requests/bulk/operation.rs

@@ -126,6 +126,9 @@ impl<TDocument> BulkOperation<Doc<TDocument>>
 where
     TDocument: Serialize,
 {
+    /**
+    Mark update as upsert request.
+    */
     pub fn doc_as_upsert(mut self) -> Self {
         if let Some(inner) = self.inner {
             self.inner = Some(inner.doc_as_upsert());