Incorrect instructions in README

[coderobe]

The README suggests /try-runtime queue [env-vars] --url ws://[kusama | westend | polkadot] [try-runtime-cli-args], however ENV vars passed to that command get interpreted as arguments to polkadot try-runtime - see paritytech/polkadot#5319 (comment)

[coderobe]

the --url parameter from that example also appears to be incorrect, the current syntax is --uri