Fixes fast vector highlighter docs per issue 24318.
The `fvh` highlighter does not support span queries. This fix updates
the docs to add a warning stating the lack of span query support for
`fvh`.
@@ -82,6 +82,10 @@ This highlighter can be used on fields with `term_vector` set to
for things like phrase matches being sorted above term matches when
highlighting a Boosting Query that boosts phrase matches over term matches
+[WARNING]
+The `fvh` highlighter does not support span queries. If you need support for
+span queries, try an alternative highlighter, such as the `unified` highlighter.
+
[[offsets-strategy]]
==== Offsets Strategy
To create meaningful search snippets from the terms being queried,
