pyre-ignore => pyrefly: ignore in error kinds doc

Reviewed By: samwgoldman

Differential Revision: D92799372

fbshipit-source-id: 03078a6a08e9065993515377a4e9f4f3088b3cef

Author: rchen152

website/docs/error-kinds.mdx

@@ -1338,6 +1338,6 @@ async def bar():
 
 ## unused-ignore
 
-This error is raised when a `# pyre-ignore` comment is not used to suppress an error, and can be safely removed.
+This error is raised when a `# pyrefly: ignore` comment is not used to suppress an error, and can be safely removed.
 
 The default severity of this diagnostic is `ignore`.