Name of the RECEIVER_ADDRESS variable

[AndreasK24]

Reading the documentation about the Receiver Contract (https://academy.avax.network/course/interchain-messaging/04-icm-basics/06-create-receiver-contract) the environment variable "RECEIVER_ADDRESS" (otherwise the user could think, that the RECEIVER_ADDRESS is the wallet address of the receiver) should be called "RECEIVER_CONTRACT_ADDRESS" (otherwise the user could think, that the RECEIVER_ADDRESS is the wallet address of the receiver) and an additional description should be added, that this variable is the place where the contract got Deployed to.