docs: add README for deadmanswitch

Author: aslushnikov

deadmanswitch/README.md

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+# DeadManSwitch
+
+DeadManSwitch is a lightweight Go program that runs a specified command with arguments and simultaneously starts a WebSocket signaling server.
+
+## Program Behavior
+
+DeadManSwitch operates with the following behavior:
+
+1. If the launched command exits, DeadManSwitch exits as well.
+2. If no client connects to the WebSocket signaling server within `DEADMANSWITCH_TIMEOUT` seconds (default is 10 seconds), the process terminates.
+3. If a client connects but then disconnects, the process terminates.
+
+## Configuration
+
+You can configure DeadManSwitch using the following environment variables:
+
+- **`DEADMANSWITCH_TIMEOUT`**: Sets the timeout (in seconds) to wait for clients to connect to the WebSocket signaling server. Default is 10 seconds.
+- **`DEADMANSWITCH_PORT`**: Specifies the port to run the server on.
+- **`DEADMANSWITCH_SUFFIX`**: Defines a suffix for the WebSocket URL endpoint.
+
+## Usage Example
+
+The following command launches `sleep 100` and accepts WebSocket connections on `ws://localhost:54321/foobar`:
+
+```bash
+DEADMANSWITCH_TIMEOUT=10 \
+DEADMANSWITCH_PORT=54321 \
+DEADMANSWITCH_SUFFIX=foobar \
+deadmanswitch sleep 100
+```
+
+## Compilation
+
+To compile, run `./build.sh`