Update README.md - mark down to markdown

[Parikshit-Hooda]

Description

changed mark down to markdown because it makes better sense.

Motivation and Context

part of hacktoberfest.

How To Test This

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Final checklist

• My change requires a change to the documentation.

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@af77716). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master       #1   +/-   ##
=========================================
  Coverage          ?   97.66%           
=========================================
  Files             ?       52           
  Lines             ?     4372           
  Branches          ?        0           
=========================================
  Hits              ?     4270           
  Misses            ?      102           
  Partials          ?        0

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update af77716...27577bd. Read the comment docs.

[Parikshit-Hooda]

@Dillon-Brown please merge this pr.

[Dillon-Brown]

@Dillon-Brown please merge this pr.

#2 (comment)