docs(opensearchapi): point the sub-client table at the authoritative catalog

The README's Sub-Clients table and the package doc (doc.go, rendered on
pkg.go.dev) both enumerate the sub-clients, risking drift. Frame the README
table as a quick-scan cheat sheet and link to the package overview's Sub-clients
section on pkg.go.dev as the authoritative catalog for the partition model,
alias fields, and name-collision semantics -- which doc.go now owns.

Also align the Client Creation password placeholder with the rest of the docs
(myStrongPassword123!).

Signed-off-by: Sean Chittenden <sean.chittenden@crowdstrike.com>

Author: sean-

opensearchapi/README.md

@@ -18,7 +18,7 @@ client, err := opensearchapi.NewClient(opensearchapi.Config{
     Client: opensearch.Config{
         Addresses: []string{"https://localhost:9200"},
         Username:  "admin",
-        Password:  "admin",
+        Password:  "myStrongPassword123!",
     },
 })
 
@@ -76,7 +76,10 @@ client.Search(ctx, nil) // searches all indices with default params
 
 ## Sub-Clients
 
-Operations are grouped into sub-clients that mirror the OpenSearch API namespaces:
+Operations are grouped into sub-clients that mirror the OpenSearch API namespaces. The table
+below is a quick-scan cheat sheet; the [package overview on pkg.go.dev](https://pkg.go.dev/github.com/opensearch-project/opensearch-go/v5/opensearchapi#hdr-Sub_clients)
+is the authoritative catalog, with the partition model, alias fields, and name-collision
+semantics.
 
 | Sub-Client                   | Example Call                                    |
 | ---------------------------- | ----------------------------------------------- |