fix(tracker): fix readme

tracker/CONTRIBUTING.md

@@ -0,0 +1,51 @@
+> ### Please use `dev` branch as base and target branch for PRs
+> ___
+
+### Tracker structure
+
+- messages are stored as definitions in [mobs](../mobs/messages) package and are auto generated
+- modules are smaller bits that expand functionality and should be used as a base for **all** new features, 
+they share similar structure as plugins:
+```ts
+// tracker/main/modules/battery.ts
+import { App } from "../app";
+import { BatteryAlert } from '../messages'
+
+export function BatteryAlertManager(sendMessage: App['send']) {
+  // do stuff, i.e
+  navigator.getBattery(battery => {
+    battery.addEventListener("levelchange", () => {
+      if (battery.level < 30) {
+        app.send(BatteryAlert(level))
+      }
+    });
+  })
+}
+
+// tracker/main/app/index.ts
+// tracker constructor
+this.batteryAlertManager = new BatteryAlertManager(this.send)
+
+```
+> Bear in mind, that for easier testing and debugging, 
+> they should only accept required methods and not the whole app. They can be represented as classes as well.
+
+- Observer is a parent class that creates MutationObserver and tracks HTML changes for base app and iframes
+- Webworker handles message batch encoding (into byte array), queueing and sending all data to server,
+- Other core modules (mouse, canvas, node counter, etc) resign in /app.
+- Plugins are functions that expand tracker functionality but are to specific to be included in the code: redux tracker, 
+vuex, zustand, assist library etc
+
+### Workflow 
+While creating a specific behavior, like addon for Redux, create a separate plugin instead of adding it to core lib.
+Plugin is a function that accepts tracker app as argument, it can return custom hook to create named state store, or handle everything inside main body.
+
+### Great examples
+
+- [Redux plugin](./tracker-redux)
+- [Tab activity module](./tracker/src/main/modules/tabs.ts)
+- [Feature flags module](./tracker/src/main/modules/featureFlags.ts)
+
+### Questions?
+
+Feel free to raise an issue or come to our [Slack](https://slack.openreplay.com)

tracker/README.md

@@ -32,4 +32,4 @@ npm install --save ../path/to/openreplay/monorepo/tracker/tracker
 
 ## Contributing notes
 
-Please use `dev` branch as base and target branch.
+read [CONTRIBUTING.md](./CONTRIBUTING.md)