link to autocomplete docs from README

Author: stringiest

README.md

@@ -6,7 +6,8 @@ AI Search][vertex-docs] ("Discovery Engine") product as its underlying search en
 two core pieces of functionality:
 - An API that is "minimally compatible" with the existing `search-api` REST interface to the extent
   necessary to power the ["site search" (`/search/all`) finder][search-all-finder].
-- A synchonisation worker that receives content updates from the Publishing API message queue and
+- An [autocomplete function](docs/search_autocomplete.md) that provides our users with helpful suggestions to complete their query as they type in search fields
+- A synchronisation worker that receives content updates from the Publishing API message queue and
   updates the Discovery Engine dataset accordingly
 
 ## Local development