Update debugging.md

Hi, we were trying to debug cloud functions locally, using functions-framework.
It seems that the doc is out of date, it doesn't work if you point to .bin folder

Author: tnovau

docs/debugging.md

@@ -19,7 +19,7 @@ npm install @google-cloud/functions-framework
 3. Run `node`, enable the inspector and run the Functions Framework:
 
 ```sh
-node --inspect node_modules/.bin/functions-framework --target=helloWorld
+node --inspect node_modules/@google-cloud/functions-framework/build/src/main.js --target=helloWorld
 ...
 Debugger listening on ws://127.0.0.1:9229/5f57f5e9-ea4b-43ce-be1d-6e9b838ade4a
 For help see https://nodejs.org/en/docs/inspector
@@ -28,6 +28,4 @@ Function: helloWorld
 URL: http://localhost:8080/
 ```
 
-> Note that the [symlinked executable](https://docs.npmjs.com/cli/v8/configuring-npm/folders#executables) of the function framework in  node_modules/**.bin**/functions-framework is used to direct the debugger to the necessary entrypoint.
-
 You can now use an IDE or other tooling to add breakpoints, step through your code and debug your function.