Added MFSN description

[stse3]

Notion Ticket

Dev Onboarding Ticket – MFSN Readme Update

Implementation description

• added MFSN description
• added my name

Steps to test

What should reviewers focus on?

Checklist

• [ x] My PR name is descriptive and in imperative tense
• [ x] My commit messages are descriptive and in imperative tense. My commits are atomic and trivial commits are squashed or fixup'd into non-trivial commits
• [x ] I have run the appropriate linter(s)
• [x ] I have requested a review from the PL, as well as other devs who have background knowledge on this PR or who will be building on top of this PR

[ericahan22]

Also make sure to add the actual Notion ticket name into the PR description

[LucasHJin]

LGTM!