doc: Added Miscellaneous section for Docker users

Added CLN image execution and testing hints for Docker users.

Changelog-None.

doc/contribute-to-core-lightning/docker-images.md

@@ -13,7 +13,7 @@ Docker Buildx is an extension of Docker's build command, that provides a more ef
    Docker CLI experimental features are required to use Buildx. Enable them by setting the DOCKER_CLI_EXPERIMENTAL environment variable to enabled.  
    You can do this by adding the following line to your shell profile file (.bashrc, .zshrc, etc.):
 
-```
+```shell
 export DOCKER_CLI_EXPERIMENTAL=enabled
 ```
 
@@ -22,7 +22,7 @@ After adding it, source your shell profile file or restart your shell to apply t
 2. Create a new builder instance  
    By default, Docker uses the "legacy" builder. You need to create a new builder instance that uses BuildKit. To create a new builder instance, use the following command:
 
-```
+```shell
 docker buildx create --use
 ```
 
@@ -33,7 +33,7 @@ The --use flag sets the newly created builder as the current one.
 1. Check Buildx is working  
    Use the `docker buildx inspect --bootstrap` command to verify that Buildx is working correctly. The `--bootstrap` option ensures the builder instance is running before inspecting it. The output should look something like this:
 
-```
+```shell
 Name:          my_builder
 Driver:        docker-container
 Last Activity: 2023-06-13 04:37:30 +0000 UTC
@@ -55,7 +55,7 @@ sudo systemctl restart docker
 
 3. Setup QEMU to run binaries from multiple architectures
 
-```
+```shell
 docker run --rm --privileged multiarch/qemu-user-static --reset -p yes
 ```
 
@@ -63,7 +63,7 @@ docker run --rm --privileged multiarch/qemu-user-static --reset -p yes
 
 Again run `docker buildx inspect --bootstrap` command to verify that `linux/arm64` is in the list of platforms.
 
-```
+```shell
 Name:          my_builder
 Driver:        docker-container
 Last Activity: 2023-06-13 04:37:30 +0000 UTC
@@ -81,3 +81,83 @@ Platforms: linux/amd64, linux/amd64/v2, linux/amd64/v3, linux/amd64/v4, linux/38
 2. Run script `tools/build-release.sh --push docker` to build `amd64`, `arm64v8`, `latest` and `multiarch` images and publish them on Dockerhub.
 
 3. If you do not want to push the images directly on Dockerhub then run `tools/build-release.sh docker`. It will only create images locally but not push them to Dockerhub.
+
+
+# Miscellaneous
+## Testing Docker image
+
+> 📘 QEMU Multiarch Setup
+> 
+> Before running a Docker image on a different platform than your local architecture, ensure that the `multiarch/qemu-user-static` setup is functioning correctly. Instructions for setting this up can be found [here](https://docs.corelightning.org/docs/docker-images#setting-up-multiarchqemu-user-static).
+
+
+The Core Lightning (CLN) Docker image (platforms: `linux/amd64`, `linux/arm64`, `linux/arm/v7`) can be tested with a local Bitcoin regtest setup using the following command:
+
+```shell
+docker run -it --rm --platform=linux/amd64 --network=host -v '/root/.lightning:/root/.lightning' -v '/root/.bitcoin:/root/.bitcoin' elementsproject/lightningd:latest --network=regtest
+```
+
+## Test repro Dockerfiles and repro-build.sh:
+1. Once the `cl-repro-<distro>` builder image is created, you can run it with:
+
+```shell
+docker run -it -v $(pwd):/repo cl-repro-noble /bin/bash
+```
+
+2. Get the Docker container ID of the above container using:
+
+```shell
+docker container ps
+```
+
+3. Start a shell in the container with:
+
+```shell
+docker exec -it <container-id-from-step2> bash
+```
+
+4. You can now run `. tools/repro-build.sh` with `--force-version` and `--force-mtime` arguments as needed.
+
+## Execute other scripts for testing:
+
+1. Create a directory named `lightning-poststart.d` in the `LIGHTNINGD_DATA` (`/root/.lightning`) directory.
+
+2. Save executable scripts in this directory.
+
+3. Run the container ensuring that:
+   - The lightning data directory is mounted.
+   - The lightning data directory path is defined with the environment variable `LIGHTNINGD_DATA`.
+
+```shell
+docker run -it --rm --platform=linux/amd64 --network=host -v '/root/.lightning:/root/.lightning' -v '/root/.bitcoin:/root/.bitcoin' -e LIGHTNINGD_DATA=/root/.lightning elementsproject/lightningd:latest --network=regtest
+
+```
+
+## Using CLI for CLN Node Running in the Docker Container
+
+### From Host (Local CLI)
+
+Use your local lightning-cli (if installed), ensuring that `lightning-dir` is configured with the local directory that is mounted to the container's `root/.lightning`.
+
+```shell
+sudo lightning-cli --regtest --lightning-dir=/root/.lightning getinfo
+```
+
+### Inside Docker Container
+1. Get the container ID for the image `elementsproject/lightningd:latest`:
+
+```shell
+docker container ps
+```
+
+2. Run a new command in the running `lightningd` container:
+
+```shell
+docker exec -it <container-id-from-step1> bash
+```
+
+3. Use the container's `lightning-cli`:
+
+```shell
+lightning-cli --regtest getinfo
+```