Added experimental annotation to the update-by-query and reindex docs

docs/reference/docs/reindex.asciidoc

@@ -1,6 +1,8 @@
 [[docs-reindex]]
 == Reindex API
 
+experimental[The reindex API is new and should still be considered experimental.  The API may change in ways that are not backwards compatible]
+
 The most basic form of `_reindex` just copies documents from one index to another.
 This will copy documents from the `twitter` index into the `new_twitter` index:
 

docs/reference/docs/update-by-query.asciidoc

@@ -1,6 +1,8 @@
 [[docs-update-by-query]]
 == Update By Query API
 
+experimental[The update-by-query API is new and should still be considered experimental.  The API may change in ways that are not backwards compatible]
+
 The simplest usage of `_update_by_query` just performs an update on every
 document in the index without changing the source. This is useful to
 <<picking-up-a-new-property,pick up a new property>> or some other online