Fix #336 : Updated Readme File

[ayyushx]

Explanation

The following my PR does :-

1. Clear Purpose and Steps: Explained the role of constants.js in handling repository-specific events and checks, with easy-to-follow steps for adding their repository to checksWhitelist.
2. Detailed Example: Provided a clear example of adding repository-specific events, allowing users to replicate the setup accurately:
   const checksWhitelist = {
   'my-repo-name': {
   [openEvent]: [claCheck],
   [PRLabelEvent]: [prLabelCheck],
   // additional events here
   }
   };
   3.Common Pitfalls and Notes: Included best practices (e.g., using lowercase repository names) and explained core constants, making it user-friendly and minimizing errors.
   By enhancing these instructions, i made it straightforward for users to configure constants.js and start the project locally.

Checklist

• [x ] I have successfully deployed my own instance of Oppiabot.
  • You can find instructions for doing this here.
• [x ] I have manually tested all the changes made in this PR following the manual tests matrix.

[HardikGoyal2003]

@seanlip PTAL! Thanks!

[seanlip]

@ayyushx Please follow the "getting started" instructions in the Oppia wiki https://github.com/oppia/oppia/wiki/Contributing-code-to-Oppia#setting-things-up -- we can't accept your PRs until you've done that.

Once you've done that, feel free to reopen this PR if you like, and we can review it. I'm closing it for now so that it doesn't get merged accidentally. Thanks!