Add docs for seabird-adventofcode-plugin

Author: belak

src/SUMMARY.md

@@ -14,7 +14,7 @@
   - [seabird-irc-backend](admin/seabird-irc-backend.md)
   - [seabird-minecraft-backend](admin/seabird-minecraft-backend.md)
 - [Plugins]()
-  - [seabird-adventofcode-plugin]()
+  - [seabird-adventofcode-plugin](admin/seabird-adventofcode-plugin.md)
   - [seabird-datadog-plugin]()
   - [seabird-github-plugin]()
   - [seabird-plugin-bundle]()

src/admin/seabird-adventofcode-plugin.md

@@ -0,0 +1,27 @@
+# seabird-adventofcode-plugin
+
+[![Static Badge](https://img.shields.io/badge/repository-blue?logo=git&label=%20&labelColor=grey&color=blue)](https://github.com/seabird-chat/seabird-adventofcode-plugin)
+[![GitHub Actions Workflow Status](https://img.shields.io/github/actions/workflow/status/seabird-chat/seabird-adventofcode-plugin/docker-publish.yml)](https://github.com/seabird-chat/seabird-adventofcode-plugin/actions/workflows/docker-publish.yml)
+
+## Dependencies
+
+- `seabird-core`
+
+## Configuration
+
+### Environment Variables
+
+{{#include _common_plugin_settings.md}}
+
+Advent of Code-specific settings
+
+- `AOC_SESSION` (required) - the session cookie, usually manually obtained from
+  a valid login. This must be updated once monthly to ensure it continues to
+  work.
+- `AOC_LEADERBOARD` (required) - leaderboard ID from Advent of Code to report
+  updates from. Note that the user the bot is logged in as must be joined to the
+  leaderboard.
+- `AOC_CHANNEL` (required) - the ID of the seabird channel which notifications
+  should be sent to.
+- `TIMESTAMP_FILE` (optional, defaults to `./aoc_timestamp.txt`) - path to the
+  file which is used to track the last timestamp we've processed from AOC.