docs(depinject): add examples (#12110)

## Description

Closes: #11944



---

### Author Checklist

*All items are required. Please add a note to the item if the item is not applicable and
please add links to any relevant follow up issues.*

I have...

- [ ] included the correct [type prefix](https://github.com/commitizen/conventional-commit-types/blob/v3.0.0/index.json) in the PR title
- [ ] added `!` to the type prefix if API or client breaking change
- [ ] targeted the correct branch (see [PR Targeting](https://github.com/cosmos/cosmos-sdk/blob/main/CONTRIBUTING.md#pr-targeting))
- [ ] provided a link to the relevant issue or specification
- [ ] followed the guidelines for [building modules](https://github.com/cosmos/cosmos-sdk/blob/main/docs/building-modules)
- [ ] included the necessary unit and integration [tests](https://github.com/cosmos/cosmos-sdk/blob/main/CONTRIBUTING.md#testing)
- [ ] added a changelog entry to `CHANGELOG.md`
- [ ] included comments for [documenting Go code](https://blog.golang.org/godoc)
- [ ] updated the relevant documentation or specification
- [ ] reviewed "Files changed" and left comments if necessary
- [ ] confirmed all CI checks have passed

### Reviewers Checklist

*All items are required. Please add a note if the item is not applicable and please add
your handle next to the items reviewed if you only reviewed selected items.*

I have...

- [ ] confirmed the correct [type prefix](https://github.com/commitizen/conventional-commit-types/blob/v3.0.0/index.json) in the PR title
- [ ] confirmed `!` in the type prefix if API or client breaking change
- [ ] confirmed all author checklist items have been addressed 
- [ ] reviewed state machine logic
- [ ] reviewed API design and naming
- [ ] reviewed documentation is accurate
- [ ] reviewed tests and test coverage
- [ ] manually tested (if applicable)

depinject/README.md

@@ -1,12 +1,91 @@
-# Cosmos SDK Dependency Injection `container` Module
+# Cosmos SDK Dependency Injection `depinject` Module
 
 ## Overview
 
-TODO
+`depinject` is a dependency injection framework for the Cosmos SDK. This module together with `core/appconfig` are meant
+to simplify the definition of a blockchain by replacing most of app.go's boilerplate code with a configuration file (YAML or JSON).
 
 ## Usage
 
-TODO
+### `depinject` example 
+
+```go
+package main
+
+import (
+	"fmt"
+
+	"cosmossdk.io/depinject"
+)
+
+type AnotherInt int
+
+func main() {
+	var (
+	  x int
+	  y AnotherInt
+	)
+
+	fmt.Printf("Before (%v, %v)\n", x, y)
+	depinject.Inject(
+		depinject.Provide(
+			func() int { return 1 },
+			func() AnotherInt { return AnotherInt(2) },
+		),
+		&x,
+		&y,
+	)
+	fmt.Printf("After (%v, %v)\n", x, y)
+}
+```
+
+### Full example in real app
+
+```go
+//go:embed app.yaml
+var appConfigYaml []byte
+
+var appConfig = appconfig.LoadYAML(appConfigYaml)
+
+func NewSimApp(
+	logger log.Logger,
+	db dbm.DB,
+	traceStore io.Writer,
+	loadLatest bool,
+	skipUpgradeHeights map[int64]bool,
+	homePath string,
+	invCheckPeriod uint,
+	encodingConfig simappparams.EncodingConfig,
+	appOpts servertypes.AppOptions,
+	baseAppOptions ...func(*baseapp.BaseApp),
+) *SimApp {
+	app := &SimApp{
+		invCheckPeriod: invCheckPeriod,
+	}
+
+	var (
+		appBuilder *runtime.AppBuilder
+		msgServiceRouter *baseapp.MsgServiceRouter
+	)
+
+	err := depinject.Inject(AppConfig,
+		&appBuilder,
+		&app.ParamsKeeper,
+		&app.CapabilityKeeper,
+		&app.appCodec,
+		&app.legacyAmino,
+		&app.interfaceRegistry,
+		&app.AccountKeeper,
+		&app.BankKeeper,
+		&app.FeeGrantKeeper,
+		&app.StakingKeeper,
+		&msgServiceRouter,
+	)
+	if err != nil {
+		panic(err)
+	}
+...
+```
 
 ## Debugging
 

depinject/inject.go

@@ -8,7 +8,7 @@ package depinject
 //
 // Ex:
 //  var x int
-//  Build(Provide(func() int { return 1 }), &x)
+//  Inject(Provide(func() int { return 1 }), &x)
 //
 // Inject uses the debug mode provided by AutoDebug which means there will be
 // verbose debugging information if there is an error and nothing upon success.