Add PWA resource (#1266)

#### What roadmap does this PR target?

- [ ] Code Change
- [x] Frontend Roadmap
- [ ] Backend Roadmap
- [ ] DevOps Roadmap
- [ ] All Roadmaps
- [ ] Guides

#### Please acknowledge the items listed below

- [x] I have discussed this contribution and got a go-ahead in an issue before opening this pull request.
- [x] This is not a duplicate issue. I have searched and there is no existing issue for this.
- [x] I understand that these roadmaps are highly opinionated. The purpose is to not to include everything out there in these roadmaps but to have everything that is most relevant today comparing to the other options listed.
- [x] I have read the [contribution docs](../contributing) before opening this PR.

#### Enter the details about the contribution

I am suggesting the addition of PWA tutorials from MDN Web Docs. Apart from basic introduction to PWAs, it has numerous helpful How-to's such as using client-side storage with IndexedDB and Web Storage API, making mobile-first and installable PWAs, enabling "add to home screen", using notifications and push API etc.

content/roadmaps/100-frontend/content/117-progressive-web-apps/readme.md

@@ -5,4 +5,5 @@ Progressive Web Apps (PWAs) are websites that are progressively enhanced to func
 <ResourceGroupTitle>Free Content</ResourceGroupTitle>
 <BadgeLink badgeText='Read' colorScheme="yellow" href='https://www.freecodecamp.org/news/what-are-progressive-web-apps/'>Progressive Web Apps for Beginners</BadgeLink>
 <BadgeLink badgeText='Read' colorScheme="yellow" href='https://web.dev/learn/pwa/'>Learn PWA</BadgeLink>
+<BadgeLink badgeTest='Read' colorScheme="yellow" href='https://developer.mozilla.org/en-US/docs/Web/Progressive_web_apps'>MDN Web Docs: Progressive Web Apps </BadgeLink>
 <BadgeLink badgeText='Watch' href='https://www.youtube.com/watch?v=sFsRylCQblw'>Build a Progressive Web App</BadgeLink>