chore: Update env.example NETWORK to encourage testnet or local usage (#664)

Signed-off-by: Ryley Mao <rymao_@outlook.com>

Author: ryleymao

.env.example

@@ -1,6 +1,6 @@
 OPERATOR_ID=<YOUR_OPERATOR_ID> #your account id, can be retrived from https://portal.hedera.com/dashboard
 OPERATOR_KEY=<YOUR_PRIVATE_KEY> #your testnet private key, can be retrieved from https://portal.hedera.com/dashboard
-NETWORK=<NETWORK> #eg testnet/previewnet/mainnet
+NETWORK=<NETWORK> #eg testnet/local/previewnet/mainnet, default to testnet or local
 
 # RECIPIENT_ID=<RECIPIENT_ID> #optional
 # RECIPIENT_KEY=<RECIPIENT_KEY>  #optional

CHANGELOG.md

@@ -17,6 +17,7 @@ This changelog is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.
 ### Changed
 - chore: validate that token airdrop transactions require an available token service on the channel (#632) 
 - chore: update local environment configuration in env.example (#649)
+- chore: Update env.example NETWORK to encourage testnet or local usage (#659)
 - chore: fix type hint for TokenCancelAirdropTransaction pending_airdrops parameter
 - chore: Moved documentation file `common_issues.md` from `examples/sdk_developers/` to `docs/sdk_developers/` for unified documentation management (#516).