refactor "About Us" page and minor UI and code fixes.

[Abhijay007]

Describe the changes you've made

improved "About us" page UI and code, fixes some minor UI bugs, and removed unused code file (about.MDX).

Describe if there is any unusual behavior (Any Warning) of your code(Write NA if there isn't)

NA

Additional context (OPTIONAL)

About US page UI :

Before

Updated UI :

screenshot 1	screenshot 2	screenshot 3

Checklist

• [x] My code follows the code style of this project.
• [x] All new and existing tests passed.
• [x] The title of my pull request is a short description of the requested changes.

Provide a Deployed link of route/page that needs to review

About Us page: https://deploy-preview-288--edu-client.netlify.app/about

[Abhijay007]

@vasudevsinghal @Abhishek-kumar09, please review this PR and please let me know if this change is valid as per the use case of the application.

[Abhishek-kumar09]

Also add mentor photo, you will find it in codeforcause/public folder.