docs: setting up env variable

Signed-off-by: Lakshya Singh <lakshay.singh1108@gmail.com>

README.md

@@ -13,6 +13,40 @@ docker volume create lightning_data
 docker compose up --build
 ```
 
+## Using Bitcoin Chains
+
+We have three possible overrides over the default `testnet` configuration in `docker-compose.yml`:
+- `docker-compose.testnet.yml`
+- `docker-compose.regtest.yml`
+- `docker-compose.mainnet.yml`
+
+To use override we have to pass it down both the config using `-f` flag:
+```
+docker compose -f docker-compose.yml -f <override_file> up --build
+```
+
+__Note__: Even while using `testnet` running using the override is recommended as that will expose the `P2P` port for `bitcoind` and `P2P` port for `lightningd` on the host.
+
+## Additional Regtest Commands
+
+We have to run these commands after bitcoind is up and running.
+
+Create Wallet:
+```
+docker container exec -it bitcoind bitcoin-cli createwallet default
+```
+
+Generate Address for node:
+```
+docker container exec -it bitcoind bitcoin-cli getnewaddress
+```
+
+Generate Blocks
+```
+docker container exec -it bitcoind bitcoin-cli generatetoaddress 50 $NODE_ADDRESS
+
+```
+
 ### References
 
 - [bitcoind](https://github.com/ruimarinho/docker-bitcoin-core/blob/master/23/alpine/Dockerfile) by @ruimarinho