Add installation instructions on README.md

Author: Bunn

README.md

@@ -13,3 +13,26 @@ If you prefer, the binary (unsigned) is [here](https://github.com/Bunn/Xgist/rel
 ![screenshot](./other/demo.gif)
 
 
+# Installation
+
+Easy way
+--------
+1. Download the (unsigned) binary [here](https://github.com/Bunn/Xgist/releases/latest) ;
+2. Unzip it and drag it to you Applications folder;
+3. Right click the Xgist.app and click 'Open';
+4. Xgist macOS app will open and install the extension;
+5. Close Xgist.app;
+5. Done.
+
+"Hard" way
+------------
+1. Clone the repo and open ``Xgist.xcodeproj``;
+2. Enable target signing for both the Application and the Source Code Extension using your own developer ID;
+3. Product > Archive;
+4. Right click archive > Show in Finder;
+5. Right click archive > Show Package Contents;
+6. Open Products/Applications;
+7. Drag ``Xgist.app`` to your Applications folder and double click on it;
+8. Xgist macOS app will open and install the extension;
+9. Close Xgist.app
+10. Done.