📝 Updated readme

Author: tofran

README.md

@@ -4,6 +4,8 @@ Send a webhook notification when someone from an Advent Of Code leaderboard solv
 
 I'm using this to track the progress of a group of friends on Discord.
 
+![Message example](https://user-images.githubusercontent.com/5692603/100946056-738cae80-34fa-11eb-833f-645b8ea2e116.png)
+
 ## Usage
 
 Just run this image periodically (at a minimum interval of 15 min):
@@ -18,6 +20,16 @@ $ docker run \
   ghcr.io/tofran/advent-of-code-leaderboard-notifier
 ```
 
+### Configuration
+
+ - `ADVENT_OF_CODE_LEADERBOARD_ID`: The unique ID of the leaderboard. It's an integer you can get from the end of leaderboard url or the prefix of the invite code.
+ - `ADVENT_OF_CODE_SESSION_ID`: Your advent of code session id.  
+    To retrieve it, go visit adventofcode.com, open developer tools > storage > cookies > copy the value of your `session` cookie.
+ - `WEBHOOK_URL`: Where to send the webhook. Can be for example a discord webhook.
+ - `ADVENT_OF_CODE_YEAR`: Optional, defaults to `2020`
+ - `CACHE_FILE`: Optional, defaults to `./cache.json`
+
+
 ## License
 
 MIT