Fix broken nav2 install-script link in the navigation section

[mmmarinho]

The navigation installation section (docs/source/navigation/installation.rst) included the nav2 install script from:

https://raw.githubusercontent.com/UoMMScRobotics/SFR_Gazebo/refs/heads/main/install_nav2.sh

which now returns 404 (so the section couldn't display/run the install commands, and the build emitted a Sphinx warning).

Fix

Point the include at the repository's own docker/gazebo_nav2/install_nav2.sh, mirroring exactly how the Gazebo section already references its sibling docker/gazebo_nav2/install_gazebo.sh:

-.. rli:: https://raw.githubusercontent.com/UoMMScRobotics/SFR_Gazebo/refs/heads/main/install_nav2.sh
+.. literalinclude:: ../../../docker/gazebo_nav2/install_nav2.sh
    :language: bash
    :lines: 5-14

The local file already contains the full apt-get install sequence the doc intends to show, so :lines: 5-14 is unchanged and the rendered output is preserved.

Verification

• Full Sphinx build succeeds (exit 0).
• The nav2 404 / SFR_Gazebo warning is gone; no SFR_Gazebo references remain in the built docs.
• The rendered navigation page now shows the local script's ros-jazzy-navigation2 / ros-jazzy-nav2-bringup / ros-jazzy-nav2-minimal-tb* / ros-jazzy-slam-toolbox commands.

[mmmarinho]

👍