Add small comments

libraries/architecture/src/main/kotlin/io/element/android/libraries/architecture/BackstackNode.kt

@@ -23,6 +23,11 @@ import com.bumble.appyx.core.node.ParentNode
 import com.bumble.appyx.core.plugin.Plugin
 import com.bumble.appyx.navmodel.backstack.BackStack
 
+/**
+ * This class is just an helper for configuring a backstack directly in the constructor.
+ * With this we can more easily use constructor injection without having a secondary constructor to create the [BackStack] instance.
+ * Can be used instead of [ParentNode] in flow nodes.
+ */
 @Stable
 abstract class BackstackNode<NavTarget : Any>(
     val backstack: BackStack<NavTarget>,

libraries/architecture/src/main/kotlin/io/element/android/libraries/architecture/FeatureEntryPoint.kt

@@ -19,8 +19,14 @@ package io.element.android.libraries.architecture
 import com.bumble.appyx.core.modality.BuildContext
 import com.bumble.appyx.core.node.Node
 
+/**
+ * This interface represents an entrypoint to a feature. Should be used to return the entrypoint node of the feature without exposing the internal types.
+ */
 interface FeatureEntryPoint
 
+/**
+ * Can be used when the feature only exposes a simple node without the need of plugins.
+ */
 interface SimpleFeatureEntryPoint : FeatureEntryPoint {
     fun createNode(parentNode: Node, buildContext: BuildContext): Node
 }