document the querystringSearchGet setting (#5206)

Co-authored-by: Steve Piercy <[email protected]>

docs/source/configuration/settings-reference.md

@@ -441,6 +441,17 @@ siteTitleFormat
         }
     ```
 
+querystringSearchGet
+    Volto uses `HTTP POST` requests to query the `@querystring-search` endpoint.
+    This can create a lot of traffic between Volto and the backend, and can also create a lot of cache misses.
+
+    By modifying this configuration setting and setting it to `true`, the endpoint queries will be executed as `HTTP GET` requests.
+    Thus any proxy cache in between Volto and the backend may cache those queries, improving your site performance.
+
+    Please be aware that this could break some other functionality in your site, or some of your queries may break, when they contain more than 2000 characters.
+    [See an explanation of character limits in URLs](https://stackoverflow.com/questions/417142/what-is-the-maximum-length-of-a-url-in-different-browsers/417184#417184).
+    Please test this setting properly before enabling in a production site.
+
 ```
 
 ## Views settings

news/5206.documentation

@@ -0,0 +1 @@
+Document the `querystringSearchGet` setting @erral