docs(in-app-messaging): note launch/foreground campaign event 1/day limit (#5703)

Co-authored-by: Mike Hardy <[email protected]>

Author: majirosstefan

.spellcheck.dict.txt

@@ -63,6 +63,7 @@ Firestore
 getIdToken
 GDPR
 GDPR-compliant
+github
 globals
 Gradle
 gradle

docs/in-app-messaging/usage/index.md

@@ -49,6 +49,10 @@ Firebase Console are automatically handled and displayed on your user's device.
 
 This module provides a JavaScript API to allow greater control of the displaying of these messages.
 
+# Limitations
+
+According to github issue https://github.com/firebase/firebase-ios-sdk/issues/4768 Firebase In-App Messaging allows only 1 campaign per day on app foreground or app launch. This limit is to prevent you from accidentally overwhelming your users with non-contextually appropriate messages. However, if you use the contextual triggers (for example: Analytics event or programmatically triggered in-app-messaging campaigns), there is no daily rate limit.
+
 ## Displaying Messages
 
 The `setMessagesDisplaySuppressed` method allows you to control when messages can/cannot be displayed. Below illustrates