Add allow-read to file-server debugger example (denoland#5282)

docs/tools/debugger.md

@@ -21,7 +21,7 @@ use [file_server.ts](https://deno.land/[email protected]/http/file_server.ts) from
 Use `--inspect-brk` flag to break execution on the first line.
 
 ```shell
-$ deno run --inspect-brk https://deno.land/[email protected]/http/file_server.ts
+$ deno run --inspect-brk --allow-read --allow-net https://deno.land/[email protected]/http/file_server.ts
 Debugger listening on ws:https://127.0.0.1:9229/ws/1e82c406-85a9-44ab-86b6-7341583480b1
 Download https://deno.land/[email protected]/http/file_server.ts
 Compile https://deno.land/[email protected]/http/file_server.ts