Add instruction to README

Author: ddavison

README.md

@@ -3,3 +3,13 @@
 A simple REST client for your favorite editor!
 
 ![example](https://raw.githubusercontent.com/ddavison/rest-client/master/images/example.gif)
+
+## How to use
+
+- Open the Command Palette (Mac: <kbd>Cmd</kbd>+<kbd>Shift</kbd>+<kbd>P</kbd> ; PC/Linux: <kbd>Ctrl</kbd>+<kbd>Shift</kbd>+<kbd>P</kbd>)
+- Search for "REST Client"
+- Open "Rest Client: Show"
+
+> You can also find the REST Client under Packages->REST Client->Show
+
+- Enter the URL, HTTP Verb, Headers and Payload (if necessary).