Document restrictions on fuzzy matching when using synonyms (elastic#40783)

Relates to elastic#25518

Author: romseygeek

docs/reference/query-dsl/match-query.asciidoc

@@ -75,6 +75,10 @@ rewritten.
 Fuzzy transpositions (`ab` -> `ba`) are allowed by default but can be disabled
 by setting `fuzzy_transpositions` to `false`.
 
+Note that fuzzy matching is not applied to terms with synonyms, as under the hood
+these terms are expanded to a special synonym query that blends term frequencies,
+which does not support fuzzy expansion.
+
 [source,js]
 --------------------------------------------------
 GET /_search