README: add GPU heat/ventilation warning; refresh stale GUI docs

- New "Heat and power" section up top: sustained 100% GPU load runs hot and
  costs power; keep good ventilation, watch temps, stop (Ctrl-C / tray Quit)
  and improve cooling if it gets hot.
- Fix docs the ldtray migration made false: no GTK/AppIndicator/libxdo to
  install (tray loads the toolkit at runtime), gui is the default build
  (--no-default-features for a pure worker), and the tray menu now shows
  GPUs, live speed, and Pause/Resume.
- Options table: add --gpus and --cache-max-gb, correct the --workdir default
  (per-user data dir), note --jobs is per-GPU.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: MagicalTux

README.md

@@ -5,17 +5,32 @@ and it quietly does distributed compute jobs in the background: it asks the
 coordinator for a chunk of work, runs it on your GPU, sends the result back, and
 repeats — forever, until you stop it. Run and forget.
 
+## ⚠️ Heat and power
+
+decryptd keeps your GPU at **full load, continuously** — that's how it does the
+work. A card pinned at 100% for hours pulls serious power and runs **hot**, and
+sustained heat is what wears graphics hardware out.
+
+- Make sure the machine has **good ventilation** and unobstructed airflow.
+  Enclosed cases, laptops, and dust-clogged fans that cope with short bursts can
+  overheat under a non-stop load.
+- Keep an eye on temperature (`nvidia-smi -l 5` on Linux, or any GPU monitor). If
+  the card runs hot, **stop decryptd** — `Ctrl-C`, or **Quit** from the tray — and
+  improve cooling before running it again.
+- Expect a higher **power bill** and a warmer room. On a laptop, run it plugged in
+  rather than on battery.
+
+If in doubt, stop it — the work is distributed, so one machine sitting out is
+completely fine.
+
 ## Requirements
 
 - A **CUDA-capable NVIDIA GPU**.
 - An **up-to-date NVIDIA driver**. No CUDA toolkit needed.
 - Linux or Windows (64-bit).
-- **Linux only:** the release binary includes the system-tray UI, so it needs
-  GTK 3 and an AppIndicator library present — `libgtk-3`,
-  `libayatana-appindicator3`, and `libxdo`. These ship with essentially every
-  desktop install. On a **headless server**, install them (e.g.
-  `apt install libgtk-3-0 libayatana-appindicator3-1 libxdo3`) or build without
-  the tray (`cargo build --release`). Windows bundles everything in the `.exe`.
+- **No GUI libraries to install.** The system tray loads whatever the desktop
+  provides at runtime, so it just works on a desktop and is silently skipped on a
+  headless server — the same binary runs either way.
 
 ## Get it
 
@@ -59,29 +74,31 @@ You normally don't need any of these.
 | Option | Default | What it does |
 | --- | --- | --- |
 | `--once` | off | Do a single chunk of work, then exit (handy for testing). |
+| `--jobs <N>` | `1` | How many chunks to run on the GPU at once, **per GPU**. |
+| `--gpus <LIST>` | all | Which GPUs to use, e.g. `--gpus 0,2`. Default: every detected GPU, each with its own work queue. |
 | `--idle-secs <N>` | `60` | How long to wait before re-checking when there's no work. |
-| `--jobs <N>` | `1` | How many chunks to run on the GPU at once. |
-| `--workdir <DIR>` | `decryptd-data` | Where to keep the download cache and scratch files. |
+| `--cache-max-gb <N>` | `20` | Cap the on-disk download cache; oldest blobs are evicted past this. |
+| `--workdir <DIR>` | per-user data dir | Where to keep the download cache, worker id, and scratch. Defaults to a per-user folder (`%LOCALAPPDATA%\decryptd` / `~/.local/share/decryptd`). |
 
 Downloading the next chunk and uploading finished results always happen in the
 background while the GPU works, so the card stays busy. `--jobs` only raises how
 many run *on the GPU* simultaneously — most setups are fine with the default.
+With more than one GPU, `--jobs` applies to each, so `--jobs 3` on 2 GPUs runs 6
+chunks in total.
 
 Run `decryptd --help` for the full list.
 
 ### System-tray mode
 
-The released binaries run as a **system-tray app** on Windows and Linux. decryptd
-sits in the tray with a right-click menu showing the version, the current status
-(*Waiting* or *Running*), and a **Quit** entry. The worker runs in the
-background exactly as above.
-
-If no tray host is available (for example a Linux box with no desktop session),
-decryptd logs a notice and falls back to running headless. Passing `--once` also
-runs headless, with no tray.
+The released binaries run as a **system-tray app** on Windows and Linux. Right-click
+the tray icon for a menu showing the version, current status (*Waiting* /
+*Running* / *Paused*), the GPU(s) in use, the live **speed** (tries per second,
+1-minute average), a **Pause/Resume** toggle, **Check for Updates**, and **Quit**.
+The worker runs in the background exactly as above.
 
-To build a **console-only** binary with no tray (and no GUI dependencies), build
-the default feature set — see [Building from source](#building-from-source).
+The tray loads the desktop's toolkit at runtime, so there are **no GUI libraries
+to install**. If no tray host is available — a headless server, or `--once` —
+decryptd logs a notice and runs without a tray.
 
 ## Building from source
 
@@ -90,13 +107,13 @@ against the driver library at build time — the binary still just needs the
 driver to run):
 
 ```sh
-cargo build --release                 # console-only, no GUI dependencies
-cargo build --release --features gui   # system-tray app (what the releases ship)
+cargo build --release                        # system-tray app (what the releases ship)
+cargo build --release --no-default-features   # pure worker, no tray
 ```
 
-The binary lands in `target/release/decryptd` (`.exe` on Windows). Building the
-`gui` feature on Linux additionally needs the GTK 3 / AppIndicator / libxdo
-development headers (`libgtk-3-dev libayatana-appindicator3-dev libxdo-dev`).
+The binary lands in `target/release/decryptd` (`.exe` on Windows). **No GUI system
+packages are needed** either way: the tray backend (`ldtray`) links nothing at
+build time and loads the platform toolkit at runtime.
 
 ## License