fix(docs): Node.js AI SDK: modelConfig --> config in readme (#765)

**Requirements**

- [ ] I have added test coverage for new or changed functionality
- [ ] I have followed the repository's [pull request submission
guidelines](../blob/main/CONTRIBUTING.md#submitting-pull-requests)
- [ ] I have validated my changes against all supported platform
versions

**Related issues**

https://launchdarkly.atlassian.net/browse/DOCS-1126

**Describe the solution you've provided**

Updated README to match current usage (`config` not `modelConfig`)

**Describe alternatives you've considered**

n/a

**Additional context**

Noticed by an LD engineer. Per offline conversation, updating PR title
to trigger a release for this, so that our npm page updates as well.

Author: mmrj

packages/sdk/server-ai/README.md

@@ -21,8 +21,7 @@
 
 ## Quick Setup
 
-This assumes that you have already installed the LaunchDarkly Node.js SDK, or a compatible edge
-SDK.
+This assumes that you have already installed the LaunchDarkly Node.js (server-side) SDK, or a compatible edge SDK.
 
 1. Install this package with `npm` or `yarn`:
 
@@ -40,7 +39,7 @@ const aiClient = initAi(ldClient);
 3. Evaluate a model configuration:
 
 ```typescript
-const config = await aiClient.modelConfig(
+const config = await aiClient.config(
   aiConfigKey!,
   context,
   { enabled: false },