Add basic seabird-discord-backend docs

src/SUMMARY.md

@@ -10,7 +10,7 @@
   - [seabird-core](admin/seabird-core.md)
   - [seabird-proxy-plugin](admin/seabird-proxy-plugin.md)
 - [Chat Backends]()
-  - [seabird-discord-backend]()
+  - [seabird-discord-backend](admin/seabird-discord-backend.md)
   - [seabird-irc-backend]()
   - [seabird-minecraft-backend]()
 - [Plugins]()

src/admin/_common_settings.md

@@ -0,0 +1,7 @@
+Common settings:
+
+- `SEABIRD_ID` (optional, defaults to `seabird`) - (TODO: determine what this is
+  and why it's not supported everywhere)
+- `SEABIRD_HOST` (required) - this is the URL of the `seabird-core` instance.
+  Most users should use `https://core.seabird.chat`
+- `SEABIRD_TOKEN` (required) - the seabird token

src/admin/seabird-discord-backend.md

@@ -0,0 +1,34 @@
+# seabird-discord-backend
+
+[![Static Badge](https://img.shields.io/badge/repository-blue?logo=git&label=%20&labelColor=grey&color=blue)](https://github.com/seabird-chat/seabird-discord-backend)
+[![GitHub Actions Workflow Status](https://img.shields.io/github/actions/workflow/status/seabird-chat/seabird-core/docker-publish.yml)](https://github.com/seabird-chat/seabird-discord-backend/actions/workflows/docker-publish.yml)
+
+## Dependencies
+
+- `seabird-core`
+
+## Configuration
+
+### Environment Variables
+
+{{#include _common_settings.md}}
+
+Discord-specific settings
+
+- `DISCORD_TOKEN` (required) - Both an
+  [application](https://discord.com/developers/docs/quick-start/getting-started)
+  and a [bot user](https://discord.com/developers/docs/topics/oauth2#bot-users)
+  must be set up in Discord, and connected to the relevant Discord server by an
+  admin on that server. The correct OAuth URL has been lost to time, but make
+  sure priviledged intents (presence, server members, and message content) are
+  enabled. Note that tokens must be prefixed with `Bot ` in order for Discord to
+  use them as a bot token.
+- `DISCORD_COMMAND_PREFIX` (optional, defaults to `!`)
+- `DISCORD_CHANNEL_MAP` (optional, defaults to empty) - a comma separated list
+  of Discord voice channels, followed by a `:` and then a channel which should
+  be notified when someone joins.
+
+## Known Issues
+
+- There is not true Discord "command" support, so all commands need to be
+  prefixed by the `DISCORD_COMMAND_PREFIX` setting.

src/admin/seabird-proxy-plugin.md

@@ -11,10 +11,14 @@
 
 ### Environment Variables
 
+{{#include _common_settings.md}}
+
+Proxy-specific settings
+
 - `PROXY_CONFIG_FILE` (required) - path to the config file for the plugin
 - `RUST_LOG` (optional, defaults to `info,seabird-proxy-plugin=debug`) - this is
   a common rust environment variable documented here because we set a default.
-  All seabird functionality is exposed under `seabird`.
+  All seabird functionality is exposed under the `seabird` logger.
 
 ### Config File