docs(bash): document env parameter in tool description

Author: taxilian

packages/opencode/src/tool/bash.txt

@@ -25,6 +25,7 @@ Before executing the command, please follow these steps:
 Usage notes:
   - The command argument is required.
   - You can specify an optional timeout in milliseconds. If not specified, commands will time out after 120000ms (2 minutes).
+  - You can specify an optional env parameter to set environment variables for the command (e.g., `env: { "MY_VAR": "value" }`). These are merged with the existing environment.
   - It is very helpful if you write a clear, concise description of what this command does in 5-10 words.
   - If the output exceeds ${maxLines} lines or ${maxBytes} bytes, it will be truncated and the full output will be written to a file. You can use Read with offset/limit to read specific sections or Grep to search the full content. Do NOT use `head`, `tail`, or other truncation commands to limit output; the full output will already be captured to a file for more precise searching.