docs(audience): add @imtbl/audience README (SDK-115)

- Adds packages/audience/sdk/README.md (no README existed before this).
- Documents both distribution channels: npm install for sites with a bundler, and `<script>` tag with the unpkg interim URL for sites without a build pipeline.
- Stubs the future cdn.immutable.com canonical URL with a note that the v1 lane will ship breaking changes only via v2.
- Covers init, full API table, AudienceConfig, consent modes, predefined event types, CSP guidance, and browser support.
- Reframes the @imtbl/pixel related-package note: distinction is feature surface (full SDK vs minimal pixel), not delivery channel — both packages support npm and `<script>` tag.

Refs SDK-115

Author: ImmutableJeffrey

packages/audience/sdk/README.md

@@ -0,0 +1,22 @@
+# About
+
+Immutable Audience is a consent-aware web SDK for event tracking and identity management, built for game studios. Use it to record typed events (sign-ups, purchases, game launches, and more), track page views, and tie player identity to events.
+
+# Installation
+
+To install this package, run the following command:
+
+```sh
+npm add @imtbl/audience
+# or
+pnpm add @imtbl/audience
+# or
+yarn add @imtbl/audience
+```
+
+# Documentation
+
+- [Tracking Pixel](https://docs.immutable.com/docs/products/audience/tracking-pixel) — sibling `@imtbl/pixel` package for drop-in page-view tracking
+- [Web SDK](https://docs.immutable.com/docs/products/audience/web-sdk) — this package (API reference, usage, integration walkthrough)
+- [REST API](https://docs.immutable.com/docs/products/audience/rest-api) — backend reference for direct integration
+- [Data dictionary](https://docs.immutable.com/docs/products/audience/data-dictionary) — predefined event names and property schemas