Update README.md

Author: augustdominik

README.md

@@ -4,8 +4,17 @@
 
 # Installation
 Using Package Manager:
+  1. Open package manager
+  2. + -> Add package from git URL
+  3. Paste: https://github.com/GucioDevs/SimpleMinMaxSlider.git#upm (remember the #upm at the end)
 
 # Usage
+
+Include namespace at the top of your script:
+```C#
+using GD.MinMaxSlider;
+```
+
 Code for the demonstration above:
 ```C#
 [MinMaxSlider(0,10)]