tmux-guide

Tmux guide for running background tasks. Use this guide when: 1. Before any tasks that can potentially run for more than 2 minutes (e.g.: package installs, many tests, model training) 2. Before any tasks that are expected to run indefinitely in the background (e.g.: web servers, port forwarding) 3. When a bash tool reports `timeout after 120000ms` 4. When the user requests to run tasks in the background