add calculator help

bot.py

@@ -72,7 +72,9 @@ class BotClient(discord.Client):
         return message.content.startswith("%")
 
     async def on_command(self, message: discord.Message):
-        match message.content.split(" "):
+        match re.split(" +", message.content):
+            case ["%calc?"], ["%calc", "?"]:
+                await message.reply(content=self._help_calculate())
             case ["%calc", *args]:
                 try:
                     calc = await self._calculate(args)
@@ -80,11 +82,19 @@ class BotClient(discord.Client):
                 except Exception as e:
                     _log.exception("running calculation")
                     await message.reply(
-                        content="```\n" + str(e) + "\n```", delete_after=30
+                        content="```\n" + str(e) + "\n```", delete_after=10
                     )
             case _:
                 _log.info(f"Unrecognised command {command}")
 
+    async def _help_calculate(self) -> str:
+        return """
+            Run Showdown damage calculations.
+            Example format:
+            `  -2 8 SpA Choice Specs Torkoal Overheat vs. 252 HP / 4+ SpD Assault Vest Abomasnow in Sun through Light Screen`
+            Supported: attacker/defender boosts, EVs, item, species; attacker ability; weather/terrain; screens.
+        """
+
     async def _calculate(self, args: list[str]) -> str:
         proc = sp.run(
             ["node", "calc_main.js", "--"] + args, stdout=sp.PIPE, stderr=sp.PIPE