Change installation steps

README.md

 
 ## Installation
 
-> You can install it on chrome/chromium from the `chrome://extensions` panel by specify the `src` dir or the `PasteTab.crx` file.
+> You can install it on chrome/chromium from the `chrome://extensions` panel by enabling the `Developper mode` and specify the `src` dir or drag'n'dropping the `PasteTab.crx` file.