Add quick start doc

README.md

@@ -1,6 +1,21 @@
 ## Grocery list bot
 Bot shows the list as buttons that can be clicked to mark the item as done
 
+## Quick start
+
+### Single user
+
+Send your list of items to [@grocery_guy_bot](https://t.me/grocery_guy_bot)
+
+### Multiple users (Shared list)
+
+1. Create a group with all the members
+2. Add [@grocery_guy_bot](https://t.me/grocery_guy_bot) to the group
+3. Make the bot admin to read all the messages
+4. Send your list of items.
+
+Note: Everything sent to the group is considered a list item, so the group cannot be used to for any other text messages
+
 
 ## TODO
 1. Write doc, screenshots, video, gif