chore: notes on usage

README.md

@@ -1,3 +1,10 @@
 # go-sdk
 
-Store SDK for Go
+Store SDK for Go
+
+## Usage
+Coming soon!
+
+NOTE: You should cache ownership per product ID.
+The SDK doesn't cache it per ID intentionally, because typically you can use quite a lot less memory by manually implementing it.
+See the example below (from MusicPlayer): (Coming Soon!)