chore: add description in readme

Author: AlexanderPrendota

README.md

@@ -1,2 +1,30 @@
-# Kotlin Playground Coursera Plugin
+# Kotlin Playground Coursera 
+Allows embedding interactive Kotlin playground to [coursera](https://www.coursera.org/) lessons.
 
+Plugin Current version: 0.0.0 :tada:
+
+## Installation
+
+1. Download [latest release](https://github.com/AlexanderPrendota/kotlin-playground-coursera-plugin/releases).
+2. Go to [coursera.org](https://www.coursera.org/)
+3. From the left sidebar, select `Admin`
+4. Find your course and click `Edit` next to the course title
+5. From the left sidebar, click Content and select `Edit Content`
+6. Find the lesson you want to add a plugin to, or create a new lesson
+7. From the `ADD ITEM` dropdown menu, select `Ungraded Plugin`
+8. Click Choose Plugin to select the plugin you want to add
+9. Click Continue and `Edit Configuration`, if needed
+10. When you’re done, click `Review & Publish`
+
+## Usage
+
+Find configuration panel on `Edit Configuration` and set code snippet:
+
+```json
+{
+  "code": "fun main(args: Array<String>) {\n println(\"Hello world\")\n}"
+}
+```
+* Default theme: `idea`.
+* Default platform: `JVM`.
+* Default kotlin version : [latest stable](https://try.kotlinlang.org/kotlinServer?type=getKotlinVersions) version.