update docs for headless mode (#3508)

* update docs for headless mode

* fix newline

* fix command parsing

* add docs

* Update README.md

* Update headless-mode.md

* empty commit

* update integration tests

---------

Co-authored-by: tobitege <10787084+tobitege@users.noreply.github.com>
Co-authored-by: Xingyao Wang <xingyao6@illinois.edu>

docs/modules/usage/how-to/headless-mode.md

@@ -0,0 +1,41 @@
+# Running in Headless Mode
+
+You can run OpenHands via a CLI, without starting the web application. This makes it easy
+to automate tasks with OpenHands.
+
+## With Python
+To run OpenHands in headless mode with Python,
+[follow the Development setup instructions](https://github.com/All-Hands-AI/OpenHands/blob/main/Development.md),
+and then run:
+
+```bash
+poetry run python -m openhands.core.main -t "write a bash script that prints hi"
+```
+
+## With Docker
+To run OpenHands in headless mode with Docker, run:
+
+```bash
+# Set WORKSPACE_BASE to the directory you want OpenHands to edit
+WORKSPACE_BASE=$(pwd)/workspace
+
+# Set LLM_API_KEY to an API key, e.g. for OpenAI or Anthropic
+LLM_API_KEY="abcde"
+
+# Set LLM_MODEL to the model you want to use
+LLM_MODEL="gpt-4o"
+
+docker run -it \
+    --pull=always \
+    -e SANDBOX_USER_ID=$(id -u) \
+    -e WORKSPACE_MOUNT_PATH=$WORKSPACE_BASE \
+    -e LLM_API_KEY=$LLM_API_KEY \
+    -e LLM_MODEL=$LLM_MODEL \
+    -v $WORKSPACE_BASE:/opt/workspace_base \
+    -v /var/run/docker.sock:/var/run/docker.sock \
+    --add-host host.docker.internal:host-gateway \
+    --name openhands-app-$(date +%Y%m%d%H%M%S) \
+    ghcr.io/all-hands-ai/openhands:main \ # TODO: pin a version here
+    python -m openhands.core.main \
+    -t "Write a bash script that prints Hello World"
+```