Update Docker instructions (#13437)

substrate/docker/README.md

@@ -5,23 +5,49 @@ There is no requirement on having Rust or any other toolchain installed but a wo
 
 Unlike the `parity/polkadot` image which contains a single binary (`polkadot`!) used by default, the image in this folder builds and contains several binaries and you need to provide the name of the binary to be called.
 
-You should refer to the .Dockerfile for the actual list. At the time of editing, the list of included binaries is:
+You should refer to the [.Dockerfile](./substrate_builder.Dockerfile) for the actual list. At the time of editing, the list of included binaries is:
 
 - substrate
 - subkey
 - node-template
 - chain-spec-builder
 
-To generate the latest parity/substrate image. Please first run:
+First, install [Docker](https://docs.docker.com/get-docker/).
+
+Then to generate the latest parity/substrate image. Please run:
 ```sh
 ./build.sh
 ```
 
+> If you wish to create a debug build rather than a production build, then you may modify the [.Dockerfile](./substrate_builder.Dockerfile) replacing `cargo build --locked --release` with just `cargo build --locked` and replacing `target/release` with `target/debug`. 
+
+> If you get an error that a tcp port address is already in use then find an available port to use for the host port in the [.Dockerfile](./substrate_builder.Dockerfile).
+
 The image can be used by passing the selected binary followed by the appropriate tags for this binary.
 
 Your best guess to get started is to pass the `--help flag`. Here are a few examples:
 
-- `docker run --rm -it parity/substrate substrate --version`
-- `docker run --rm -it parity/substrate subkey --help`
-- `docker run --rm -it parity/substrate node-template --version`
-- `docker run --rm -it parity/substrate chain-spec-builder --help`
+- `./run.sh substrate --version`
+- `./run.sh subkey --help`
+- `./run.sh node-template --version`
+- `./run.sh chain-spec-builder --help`
+
+Then try running the following command to start a single node development chain using the Substrate Node Template binary `node-template`:
+
+```sh
+./run.sh node-template --dev --ws-external
+```
+
+Note: It is recommended to provide a custom `--base-path` to store the chain database. For example:
+
+```sh
+# Run Substrate Node Template without re-compiling
+./run.sh node-template --dev --ws-external --base-path=/data
+```
+
+> To print logs follow the [Substrate debugging instructions](https://docs.substrate.io/test/debug/).
+
+```sh
+# Purge the local dev chain
+./run.sh node-template purge-chain --dev --base-path=/data -y
+```