Add instance storage to the feature matrix

Author: keithduncan

README.md

@@ -51,6 +51,7 @@ CloudWatch Logs Agent | ✅ | ✅
 Per-Instance Bootstrap Script | ✅ | ✅ 
 🧑‍🔬 git-mirrors experiment | ✅ | ✅ 
 SSM Access | ✅ | ✅ 
+Instance Storage (NVMe) | ✅ | 
 SSH Access | ✅ | 
 Periodic authorized_keys Refresh | ✅ | 
 Periodic Instance Health Check | ✅ |