Update request-body.asciidoc

Added link from `timeout` to time-units

Closes #6361

docs/reference/search/request-body.asciidoc

@@ -51,7 +51,7 @@ And here is a sample response:
 |Name |Description
 |`timeout` |A search timeout, bounding the search request to be executed
 within the specified time value and bail with the hits accumulated up to
-that point when expired. Defaults to no timeout.
+that point when expired. Defaults to no timeout. See <<time-units>>.
 
 |`from` |The starting from index of the hits to return. Defaults to `0`.