docs(readme): add credentials setup instructions

[GabrielgsdCIUwU]

Added instructions for creating a credentials.js file in the project root, including clientId and clientSecret setup. Also included a link to GitHub's official documentation on creating GitHub apps.

[febinbellamy]

Hi Gabriel, thanks so much for the PR - your changes look great. I’ll need to make a small tweak so that it integrates a little bit better with step 4, and then we'll be all set to merge!

[GabrielgsdCIUwU]

Hi Febin, that sounds good to me ^^

[febinbellamy]

Hi Gabriel, please fetch the latest changes by running the following commands:

git pull origin patch-1
git push origin patch-1

This will update your local patch-1 branch with the latest changes. Once you've pulled these updates, we will be able to see them in the pull request. After that, I'll go ahead and merge the PR. Let me know if you have any questions or if you encounter any issues updating your branch. Thanks!

[GabrielgsdCIUwU]

Hi Febin, I just updated the latest changes directly from Github. Let me know if there's anything else you need me to do.
Thanks!