✨ add plugin metadata to builtin plugins (#2113)

nonebot/plugins/echo.py

@@ -1,7 +1,18 @@
+from nonebot import on_command
 from nonebot.rule import to_me
 from nonebot.adapters import Message
 from nonebot.params import CommandArg
-from nonebot.plugin import on_command
+from nonebot.plugin import PluginMetadata
+
+__plugin_meta__ = PluginMetadata(
+    name="echo",
+    description="重复你说的话",
+    usage="/echo [text]",
+    type="application",
+    homepage="https://github.com/nonebot/nonebot2/blob/master/nonebot/plugins/echo.py",
+    config=None,
+    supported_adapters=None,
+)
 
 echo = on_command("echo", to_me())