Installation instructions for clients added

Author: vovayatsyuk

README.md

@@ -1,6 +1,20 @@
 # Easy Tabs
 
-### Installation
+## Installation
+
+### For clients
+
+There are several ways to install extension for clients:
+
+ 1. If you've bought the product at Magento's Marketplace - use
+    [Marketplace installation instructions](https://docs.magento.com/marketplace/user_guide/buyers/install-extension.html)
+ 2. Otherwise, you have two options:
+    - Install the sources directly from [our repository](https://docs.swissuplabs.com/m2/extensions/easytabs/installation/composer/) - **recommended**
+    - Download archive and use [manual installation](https://docs.swissuplabs.com/m2/extensions/easytabs/installation/manual/)
+
+### For developers
+
+Use this approach if you have access to our private repositories!
 
 ```bash
 cd <magento_root>