Add Readme for docker testnet

testnet/README.md

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+# Docker Compose Testnet for Nomos
+
+The Nomos Docker Compose Testnet contains four distinct service types:
+
+- **Bootstrap Node Service**: A singular Nomos node with its own service and a deterministic DNS address. Other nodes utilize this as their initial peer.
+- **Libp2p Node Services**: Multiple dynamically spawned Nomos nodes that announce their existence through etcd.
+- **Etcd Service**: A container running an etcd instance.
+- **Mix-Node-{0,1,2}**: These are statically configured mixnet nodes. Every Libp2p node includes these in its topology configuration.
+
+## Building
+
+Upon making modifications to the codebase or the Dockerfile, the Nomos images must be rebuilt:
+
+```bash
+docker compose build
+```
+
+## Configuring
+
+Configuration of the Docker testnet is accomplished using the `.env` file. An example configuration can be found in `.env.example`.
+
+To adjust the count of Nomos nodes, modify the variable:
+
+```bash
+DOCKER_COMPOSE_LIBP2P_REPLICAS=100
+```
+
+## Running
+
+Initiate the testnet by executing the following command:
+
+```bash
+docker compose up
+```
+
+This command will merge all output logs and display them in Stdout. For a more refined output, it's recommended to first run:
+
+```bash
+docker compose up -d
+```
+
+Followed by:
+
+```bash
+docker compose logs -f {bootstrap,libp2p-node,mixnode,etcd}
+```
+
+## Using testnet
+
+Bootstrap node is accessible from the host via `3000` and `8080` ports. To expose other nomos nodes, please update `libp2p-node` service in the `compose.yml` file with this configuration:
+
+```bash
+  libp2p-node:
+    ports:
+    - "3001-3010:3000" # Use range depending on the number of nomos node replicas.
+    - "8081-8190:8080"
+```
+
+After running `docker compose up`, the randomlly assigned ports can be viewed with `ps` command:
+
+```bash
+docker compose ps 
+```