add Flags SDK README (#1100)

Adds a README to the Flags SDK

flags-sdk/README.md

@@ -0,0 +1,11 @@
+# Flags SDK
+
+The [Flags SDK](https://flags-sdk.dev/) is a free, open-source library for using feature flags in Next.js and SvelteKit.
+
+Examples in this folder use the Flags SDK combined with different flag and experimentation providers to implement an ecommerce example application.
+
+Examples are further set up to integrate with [Flags Explorer](https://vercel.com/docs/workflow-collaboration/feature-flags/using-vercel-toolbar), which allows overridding feature flags and experiments for the current session.
+
+### Template
+
+The starting point for these provider specific examples is maintained [in the Flags SDK repository](https://github.com/vercel/flags/tree/main/examples/shirt-shop).