Update README.md

add important notice re: Graypaper v1.0

README.md

@@ -6,6 +6,10 @@
 
 # JAM Prize Milestone Delivery
 
+ℹ️⚠️ IMPORTANT NOTICE FOR JAM IMPLEMENTERS ⚠️ℹ️
+
+Please note that **no milestone submission will be accepted** until Graypaper v1.0 is available. You can track the latest releases by watching this repository: https://github.com/gavofyork/graypaper
+
 ## Process
 
 Prior to submitting your first milestone, please make sure that you have successfully completed a [KYB](https://in.sumsub.com/idensic/l/#/uni_LhZH9SdrmtuvGnnz) (or, if you work alone, a [KYC](https://in.sumsub.com/idensic/l/#/uni_ZUSbgdezo6hdrZVn)) check.