docs: install.rst + top README catch up to the 2-variant Docker

Both files still showed the old single-variant build.sh example
('./build.sh ... tags uniros:noetic'). Update both to show the
default and --slim invocations side-by-side, and add the explicit
"if you're already on Ubuntu 20.04, skip Docker" guidance — there's
a real cost (GL passthrough + nvidia-container-toolkit / driver
compatibility on 20.04 hosts) to going through Docker when the
native installer is right there.

Author: ncbdrck

README.md

@@ -44,19 +44,30 @@ piece-by-piece.
 
 If your host is Ubuntu 22.04 / 24.04, has a GPU with no Ubuntu 20.04
 driver (RTX 50-series, etc.), or is Windows with WSL2, the same
-stack ships as a Docker image:
+stack ships as a Docker image in two variants:
 
 ```bash
 git clone -b gymnasium https://github.com/ncbdrck/UniROS.git
 cd UniROS/docker
-./build.sh         # tags 'uniros:noetic'
-./run.sh           # headless
-./run_gui.sh       # GUI (Gazebo, RViz) via rocker
+
+# Default (CUDA-runtime base, ~16 GB)
+./build.sh
+./run_gui.sh
+
+# — or — slim (no CUDA in image, ~12 GB; matches the TIAGo pattern)
+./build.sh --slim
+./run_gui.sh -t uniros:noetic-slim
 ```
 
+If you're **already running Ubuntu 20.04 natively**, skip Docker and
+use the one-shot installer above on the host directly. Native install
+is faster, smaller, and avoids GL-passthrough / nvidia-container-toolkit
+compatibility quirks that have surfaced on 20.04 hosts with newer
+NVIDIA driver branches.
+
 See [`docker/README.md`](docker/README.md) and the
 [install guide's Docker section](https://uniros.readthedocs.io/en/latest/guides/install.html#option-c-docker)
-for hardware passthrough, GPU notes, and bind-mounting a host
+for variant comparison, hardware passthrough, GPU notes, and bind-mounting a host
 workspace for active development.
 
 

docs/guides/install.rst

@@ -324,18 +324,32 @@ Option C — Docker
 
 If your host can't run Ubuntu 20.04 natively (modern OEM laptop,
 Ubuntu 22.04 / 24.04, a GPU + driver stack with no Ubuntu 20.04
-support, or Windows with WSL2), the same stack is available as a
-Docker image:
+support, or Windows with WSL2), the same stack ships as a Docker
+image in two variants:
 
 .. code-block:: bash
 
    git clone -b gymnasium https://github.com/ncbdrck/UniROS.git
    cd UniROS/docker
-   ./build.sh         # 30–60 min first build; tags 'uniros:noetic'
-   ./run.sh           # headless
-   ./run_gui.sh       # GUI (Gazebo, RViz) via rocker
 
-See :doc:`docker` for the full Docker reference — when to use it,
+   # Default (CUDA-runtime base, ~16 GB)
+   ./build.sh
+   ./run_gui.sh
+
+   # — or — slim (no CUDA in image, ~12 GB; matches the TIAGo pattern)
+   ./build.sh --slim
+   ./run_gui.sh -t uniros:noetic-slim
+
+.. note::
+
+   If you're **already running Ubuntu 20.04 natively**, use Option A
+   or B above on the host directly — skip Docker. The native path is
+   faster, smaller, and avoids GL-passthrough / nvidia-container-toolkit
+   compatibility quirks that have surfaced on 20.04 hosts with newer
+   NVIDIA driver branches. Docker is for hosts that *can't* install
+   20.04 natively.
+
+See :doc:`docker` for the full Docker reference — variant comparison,
 hardware passthrough (USB and network), GPU, bind-mounting a host
 workspace for active development, troubleshooting, and the roadmap
 for in-progress features.