[docs] guide: document current Looking Glass features

doc/install_idd.rst

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+.. _installing_idd:
+
+Looking Glass IDD
+#################
+
+.. _install_idd:
+
+The Looking Glass IDD is the recommended Windows frame producer. Download the
+``looking-glass-idd-setup.exe`` installer that matches the client release, run
+it as an administrator inside the Windows guest and follow the installer.
+
+The installer includes the display driver, direct input driver and IDD helper.
+It can also install the IVSHMEM driver. If the legacy Host service is present,
+allow the installer to disable it so that only one Looking Glass producer is
+active.
+
+The display may briefly disappear while Windows installs or reloads the
+driver. Restart Windows if the installer requests it.
+
+Install
+-------
+
+1. Download the IDD installer from the same release as the client source.
+2. Run ``looking-glass-idd-setup.exe`` as an administrator in Windows.
+3. Select **IVSHMEM Driver** if a suitable IVSHMEM driver is not already
+   installed in the guest.
+4. Leave **Indirect Display Driver (IDD)** selected.
+5. If offered, leave **Disable old host app** selected. Running two producers
+   against the same shared-memory device is not supported.
+6. Complete the installation and restart Windows if requested.
+
+After installation, Windows should show a display named Looking Glass and the
+IDD helper should appear in the notification area. The helper icon reports
+whether the IDD is using GPU acceleration or software processing.
+
+The IDD installer also installs its direct input driver. There is no separate
+input package to install.
+
+Upgrade
+-------
+
+Close active clients and OBS sources, then run the new matching IDD installer
+over the existing installation. Upgrade the Linux client and OBS plugin to the
+same release before using them again.
+
+Windows may briefly remove and recreate the virtual display. Restart Windows
+when the installer reports that a restart is required.
+
+Uninstall
+---------
+
+Remove **Looking Glass (IDD)** from Windows **Installed apps** or **Programs
+and Features**. This removes both the display and input drivers and deletes
+custom IDD modes and preferences. The optional IVSHMEM files are removed from
+the Looking Glass installation directory, but an IVSHMEM driver package that
+was already installed in Windows is not uninstalled.
+
+If you are returning to the legacy Host Application, re-enable or reinstall
+its service only after the IDD has been removed.
+
+Silent installation
+-------------------
+
+The installer accepts these options for managed installations:
+
+``/S``
+   Install silently. The uppercase spelling is required.
+
+``/ivshmem``
+   Install the bundled IVSHMEM driver when it is present in the installer.
+
+``/D=path``
+   Change the installation directory. This must be the final option and must
+   not be quoted.
+
+Configuration and diagnostics
+-----------------------------
+
+.. toctree::
+   :maxdepth: 1
+
+   idd_configuration
+
+For faults, the helper can open the IDD log directory directly. See
+:ref:`idd_diagnostics` for the files to collect.