Add documentation for private geth network with Docker

docs/PRIVATE_NET_DOCKER.md

@@ -0,0 +1,29 @@
+# Running a simple private geth network with Docker
+
+This document shows a minimal example of running a single-node private
+geth network using Docker. It is intended for local experiments and
+should not be used as-is in production.
+
+## Example `docker-compose.yml`
+
+```yaml
+version: "3.8"
+
+services:
+  geth:
+    image: ethereum/client-go:stable
+    container_name: geth-private
+    command:
+      [
+        "--http",
+        "--http.addr=0.0.0.0",
+        "--http.api=eth,net,web3,personal",
+        "--dev",
+        "--dev.period=0",
+        "--verbosity=3"
+      ]
+    ports:
+      - "8545:8545"
+      - "30303:30303"
+    volumes:
+      - ./data:/root/.ethereum