Added Cog example

Author: eunwoo1104

README.md

@@ -2,6 +2,7 @@
 Simple Discord Slash Command extension for [discord.py](https://github.com/Rapptz/discord.py).
 
 ## Example
+Normal usage:
 ```py
 import discord
 from discord.ext import commands
@@ -21,6 +22,33 @@ async def _test(ctx: SlashContext):
 bot.run("discord_token")
 ```
 
+Cog:
+```py
+import discord
+from discord.ext import commands
+from discord_slash import SlashCommand
+from discord_slash import SlashContext
+
+
+class Slash(commands.Cog):
+    def __init__(self, bot):
+        self.bot = bot
+        self.slash = SlashCommand(bot, override_type=True)
+        # Cog is only supported by commands ext, so just skip checking type.
+
+        @self.slash.slash(name="test")
+        async def _test(ctx: SlashContext):
+            await ctx.send(content="Hello, World!")
+
+    def cog_unload(self):
+        self.slash.remove()
+
+
+def setup(bot):
+    bot.add_cog(Slash(bot))
+
+```
+
 ## Installation
 `pip install -U discord-py-slash-command`