fill readme + rename fallback state handler

README.md

@@ -16,3 +16,28 @@ You can create your bot using
 
 That is a set of libraries for plagubots. Look at the
 [PlaguBot Plugin template](https://insanusmokrassar.github.io/PlaguBotPluginTemplate/) to find how to create your bot.
+
+### Technical help
+
+In this bot has been used variant with FSM. That means that you may use all the [Behaviour Builder with FSM](https://bookstack.inmo.dev/books/telegrambotapi/page/behaviour-builder-with-fsm) functionality. In case you wish to setup states repo, you should use the next code in the `setupDI` of your plugin:
+
+```kotlin
+single<StatesManager<State>> {
+    // setup your manager and return here
+    // Default is:
+    DefaultStatesManager(
+        InMemoryDefaultStatesManagerRepo()
+    )
+}
+```
+
+Besides, you may setup handling errors lambda in the same function:
+
+```kotlin
+single<StateHandlingErrorHandler<State>> {
+    { state, e ->
+        logger.eS(e) { "Unable to handle state $state" } // logging by default
+        null // you should return new state or null, default callback will return null
+    }
+}
+```