Add documentation for tlBMC Install Module onboarding.

This new guide explains how to enable and configure the Install Module for NPIs.
The overview page is updated to link to this new module documentation.

PiperOrigin-RevId: 820476761
Change-Id: I5fab5a834ac9cba776b8061fff3d77b63baa350e
diff --git a/tlbmc/g3doc/onboarding_npis/install_module.md b/tlbmc/g3doc/onboarding_npis/install_module.md
new file mode 100644
index 0000000..88a4079
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+++ b/tlbmc/g3doc/onboarding_npis/install_module.md
@@ -0,0 +1,49 @@
+# Onboarding NPIs to Install Module
+
+<!--*
+# Document freshness: For more information, see go/fresh-source.
+freshness: { owner: 'tlbmc-dev' reviewed: '2025-10-15' }
+*-->
+
+This document describes how to enable and configure the tlBMC Install Module
+for an NPI. This module enables firmware updates through Redfish, including
+support for firmware bundle updates via multipart HTTP push updates.
+
+[TOC]
+
+## Prerequisites
+
+To use the Install Module, it must be enabled for your platform in
+`tlbmc_config_bundle.textproto`. If it is not enabled, tlBMC will not expose
+the necessary Redfish routes for firmware updates.
+See `tlbmc_config_bundle.textproto` in tlbmc source.
+
+To enable the module, add `install_module { enabled: true }` to your
+platform's configuration in `platform_to_config` map. For example:
+
+```textproto
+platform_to_config {
+  key: "your_platform_name"
+  value {
+    install_module {
+      enabled: true
+    }
+  }
+}
+```
+
+## Functionality
+
+When the Install Module is enabled, tlBMC takes ownership of Redfish routes
+related to firmware updates and task monitoring. Specifically, it enables:
+
+*   **/redfish/v1/UpdateService**: This service provides Redfish endpoints for
+    firmware updates. The module supports firmware bundle updates, typically
+    performed by POSTing to an endpoint under UpdateService with content-type
+    `multipart/form-data`.
+*   **/redfish/v1/TaskService**: This service allows clients to monitor the
+    progress of long-running operations, such as firmware updates initiated
+    through the UpdateService.
+
+These services work together to provide a standard Redfish interface for
+initiating and monitoring firmware updates on the BMC.
diff --git a/tlbmc/g3doc/onboarding_npis/overview.md b/tlbmc/g3doc/onboarding_npis/overview.md
index 1822690..fb97551 100644
--- a/tlbmc/g3doc/onboarding_npis/overview.md
+++ b/tlbmc/g3doc/onboarding_npis/overview.md
@@ -57,6 +57,7 @@
 -   [Fru Collector Module](fru_collector_module.md)
 -   [Sensor Collector Module](sensor_collector_module.md)
 -   [Metric Collector Module](metric_collector_module.md)
+-   [Install Module](install_module.md)
 
 ## tlBMC Configuration