Add docstring to action_check_bindings (#2266)

* Add docstring to action_check_bindings

* Use action docstring convention

src/textual/app.py

@@ -2448,6 +2448,7 @@ class App(Generic[ReturnType], DOMNode):
         self._unregister(root)
 
     async def action_check_bindings(self, key: str) -> None:
+        """An [action](/guide/actions) to handle a key press using the binding system."""
         if not await self.check_bindings(key, priority=True):
             await self.check_bindings(key, priority=False)
 
@@ -2455,9 +2456,6 @@ class App(Generic[ReturnType], DOMNode):
         """An [action](/guide/actions) to quit the app as soon as possible."""
         self.exit()
 
-    async def action_bang(self) -> None:
-        1 / 0
-
     async def action_bell(self) -> None:
         """An [action](/guide/actions) to play the terminal 'bell'."""
         self.bell()