Document usage in readme

packages/adapter-launchdarkly/README.md

@@ -0,0 +1,41 @@
+# `@flags-sdk/launchdarkly`
+
+## Usage
+
+**NOTE:** [The LaunchDarkly Vercel integration must be installed on our account.](https://vercel.com/integrations/launchdarkly)
+
+The following environment variables are required in order to use the default adapter:
+
+```sh
+export EDGE_CONFIG="https://edge-config.vercel.com/ecfg_abdc1234?token=xxx-xxx-xxx" # Provided by Vercel when connecting an Edge Config to the project
+export LD_CLIENT_SIDE_KEY="612376f91b8f5713a58777a1"
+export LD_PROJECT_SLUG="my-project"
+```
+
+```ts
+import { launchDarkly, type LDContext } from '@flags-sdk/launchdarkly';
+
+const identify = dedupe(async (): Promise<LDContext> => {
+  return {
+    key: 'user_123',
+  };
+});
+
+export const showBanner = flag<boolean, LDContext>({
+  key: 'show-banner',
+  identify,
+  adapter: launchDarkly(),
+});
+```
+
+It's possible to create an adapter by using the `createLaunchDarklyAdapter` function:
+
+```ts
+import { createLaunchDarklyAdapter } from '@flags-sdk/launchdarkly';
+
+const adapter = createLaunchDarklyAdapter({
+  ldProject: 'my-project',
+  ldClientSideKey: '612376f91b8f5713a58777a1',
+  edgeConfigConnectionString: process.env.EDGE_CONFIG,
+});
+```