Add compatibility table for clients

Sample code is commented out, but included to help contributors verify compatibility.

_clients/index.md

@@ -0,0 +1,80 @@
+---
+layout: default
+title: Compatibility
+nav_order: 1
+has_children: false
+redirect_from:
+  - /clients/
+---
+
+# OpenSearch client compatibility
+
+Most clients that work with Elasticsearch OSS 7.10.2 *should* work with OpenSearch, but the latest versions of those clients might include license or version checks that artificially break compatibility. This page includes recommendations around which versions of those clients to use for best compatibility with OpenSearch.
+
+Client | Recommended version
+:--- | :---
+Java low-level REST client | 7.13.4
+Java high-level REST client | 7.13.4
+Python Elasticsearch client | 7.13.4
+Elasticsearch Node.js client | 7.13.0
+
+
+{% comment %}
+## Python 3 test code
+
+This code indexes a single document and is equivalent to `PUT /python-test-index1/_doc/1`.
+
+```python
+from elasticsearch import Elasticsearch
+
+host = 'localhost'
+port = 9200
+# For testing only. Do not store credentials in code.
+auth = ('admin', 'admin')
+
+es = Elasticsearch(
+  hosts = [{'host': host, 'port': port}],
+  http_auth = auth,
+  use_ssl = True,
+  verify_certs = False
+)
+
+document = {
+  "title": "Moneyball",
+  "director": "Bennett Miller",
+  "year": "2011"
+}
+
+response = es.index(index='python-test-index1', id='1', body=document, refresh=True)
+
+print(response)
+```
+
+
+## Node.js test code
+
+This code is equivalent to `GET /`.
+
+```js
+const { Client } = require('@elastic/elasticsearch')
+const client = new Client({
+  node: 'https://localhost:9200',
+  auth: {
+    // For testing only. Don't store credentials in code.
+    username: 'admin',
+    password: 'admin'
+  },
+  ssl: {
+    // ca: fs.readFileSync('./cacert.pem'),
+    rejectUnauthorized: false
+  }
+})
+
+async function run () {
+  const { body } = await client.info();
+  console.log(body);
+}
+
+run().catch(console.log)
+```
+{% endcomment %}