docs: fix Docker example to use regtest env vars consistently

README.md

@@ -28,8 +28,8 @@ docker run -d \
   --tmpfs /tmp:rw,noexec,nosuid \
   -v /path/to/data:/var/bal:rw \
   -v /path/to/.bitcoin/regtest/.cookie:/var/bal/.bitcoin/regtest/.cookie:ro \
-  -e BAL_SERVER_BITCOIN_ADDRESS="your_xpub_or_address" \
-  -e BAL_SERVER_BITCOIN_FIXED_FEE=50000 \
+  -e BAL_SERVER_REGTEST_ADDRESS="your_xpub_or_address" \
+  -e BAL_SERVER_REGTEST_FIXED_FEE=50000 \
   -e BAL_SERVER_INFO="BAL server" \
   -e BAL_PUSHER_NETWORK=regtest \
   -e BAL_PUSHER_REGTEST_ZMQ_HASHBLOCK=tcp://127.0.0.1:28332 \