Add In-App Forms to README

[belleklaviyo]

Description

https://klaviyo.atlassian.net/browse/CHNL-16763

Read the formatted README here

[dan-peluso]

Suggested change

[In-app forms](https://help.klaviyo.com/hc/en-us/articles/34567685177883) are messages displayed to mobile app users while they are actively using an app. You can create new in-app forms in a drag-and-drop editor in the Sign-Up Forms tab in Klaviyo. Follow the instructions in this section to integrate forms with your app. The SDK will display forms according to their targeting and behavior settings and collect delivery and engagement analytics automatically.

[In-app forms](https://help.klaviyo.com/hc/en-us/articles/34567685177883) are popups displayed to mobile app users while they are actively using an app. You can create new in-app forms in a drag-and-drop editor in the Sign-Up Forms tab in Klaviyo. Follow the instructions in this section to integrate forms with your app. The SDK will display forms according to their targeting and behavior settings and collect delivery and engagement analytics automatically.

[dan-peluso]

I think we're going to need some sort of section on setup for Android - we need to let them know that they have to call

Applcation.onCreate() {
    Klaviyo.registerForLifecycleCallbacks(this)
}

in the native layer (unless they are initializing the Klaviyo SDK from the native layer in the Application onCreate) or else in app forms won't work. @evan-masseau any thoughts on that copy? Definitely want to make it obvious that this is required on Android.

[evan-masseau]

Something like this for android:

Suggested change

	#### Android
	In your Application class you **must** call `Klaviyo.registerForLifecycleCallbacks(applicationContext)`, due to timing issues, this cannot be achieved from the RN layer at this time.
	```kotlin
	// Application subclass
	import android.app.Application
	import com.klaviyo.analytics.Klaviyo
	class YourApplication : Application() {
	override fun onCreate() {
	super.onCreate()
	/* ... */
	// Initialize is required before invoking any other Klaviyo SDK functionality
	Klaviyo.initialize("KLAVIYO_PUBLIC_API_KEY", applicationContext)
	// If unable to call initialize, you must at least register lifecycle listeners:
	Klaviyo.registerForLifecycleCallbacks(applicationContext)
	}

this suggestion block won't quite work because of nested back ticks :( ```