Added list of available prexifes to ?help

- Only shows when more then one is available.

Fixes #353

CHANGELOG.md

@@ -7,6 +7,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 ## [Unreleased]
 ### Added
 - MUF and foF2 maps from [prop.kc2g.com](https://prop.kc2g.com/).
+- The list of available prefixes to `?help` when there is more than one.
 ### Changed
 - New colour theme for `?greyline`.
 - Moved great circle distance and bearing calculation from `?ungrid` to `?griddistance`.

exts/base.py

@@ -61,6 +61,9 @@ class QrmHelpCommand(commands.HelpCommand):
         embed.title = "qrm Help"
         embed.description = (f"For command-specific help and usage, use `{self.context.prefix}help [command name]`."
                              " Many commands have shorter aliases.")
+        if isinstance(self.context.bot.command_prefix, list):
+            embed.description += (" All of the following prefixes work with the bot: `"
+                                  + "`, `".join(self.context.bot.command_prefix) + "`.")
         mapping = await mapping
 
         for cat, cmds in mapping.items():