docs: Add docs for setting store loader (#9526)

## Description

Closes: #9503 

<!-- Add a description of the changes that this PR introduces and the files that
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Add documentation for setting StoreLoader as part of in-place store migration.

---

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docs/building-modules/upgrade.md

@@ -8,7 +8,7 @@ In-place store migrations allow your modules to upgrade to new versions that inc
 
 ## Prerequisite Readings
 
-- [In-Place Store Migration](../core-concepts/upgrade.md) {prereq}
+- [In-Place Store Migration](../core/upgrade.md) {prereq}
 
 ## Consensus Version
 

docs/core/upgrade.md

@@ -82,6 +82,29 @@ To learn more about configuring migration scripts for your modules, see the [Mig
 
 You can introduce entirely new modules to the application during an upgrade. New modules are recognized because they have not yet been registered in `x/upgrade`'s `VersionMap` store. In this case, `RunMigrations` calls the `InitGenesis` function from the corresponding module to set up its initial state.
 
+### Add StoreUpgrades for New Modules
+
+All chains preparing to run in-place store migrations will need to manually add store upgrades for new modules and then configure the store loader to apply those upgrades. This ensures that the new module's stores are added to the multistore before the migrations begin.
+
+```golang
+upgradeInfo, err := app.UpgradeKeeper.ReadUpgradeInfoFromDisk()
+if err != nil {
+	panic(err)
+}
+
+if upgradeInfo.Name == "my-plan" && !app.UpgradeKeeper.IsSkipHeight(upgradeInfo.Height) {
+	storeUpgrades := storetypes.StoreUpgrades{
+		// add store upgrades for new modules
+		// Example: 
+		//    Added: []string{"foo", "bar"},
+		// ...
+	}
+
+	// configure store loader that checks if version == upgradeHeight and applies store upgrades
+	app.SetStoreLoader(upgradetypes.UpgradeStoreLoader(upgradeInfo.Height, &storeUpgrades))
+}
+```
+
 ## Overwriting Genesis Functions
 
 The Cosmos SDK offers modules that the application developer can import in their app. These modules often have an `InitGenesis` function already defined.