Update Step 3 on README.md

the dfx.json proposes a list of cannisters, so if you don't specify which canister you refeer you won't be able to pass the argument as you'll get the following error:
Error: The init argument can only be set when deploying a single canister.

rust/dip721-nft-container/README.md

@@ -115,7 +115,7 @@ dfx start --background --clean
 
 Deploy the canister with the command:
 ```sh
-dfx deploy --no-wallet --argument \
+dfx deploy dip721_nft_container --no-wallet --argument \
 "(record {
     name = \"Numbers One Through Fifty\";
     symbol = \"NOTF\";