Replace README.txt with README.md

Hi please the patch

After applying the patch, readme.txt file is removed

Reviewed! Patch 2 worked for me. Thanks!

@Nupur Badola
Adding a screenshot of a patch applying does not add any value, please don't do this.

@dineshkumarbollu
The patch in 2 only removes the .txt but adds no new .md file?

@Jaspreet-Kaur
What do you mean the patch works? Nothing about this is functional so how can it even work? Since there are only removed lines in the patch, nothing actually happens?

---

If the maintainers want to move the file to markdown, there is a gain in doing this, but I would suggest not crediting anyone for the change.

Created MR for the change. Please review.

Reviewed MR!2, the patch is not cleanly applied.

1. Use "##Table of contents" instead of "## CONTENTS OF THIS FILE".
2. Use - (hyphen) instead of * (asterisk).
3. Use the format : 
For a full description of the module, visit the
[project page](https://www.drupal.org/project/admin_menu).

Submit bug reports and feature suggestions, or track changes in the
[issue queue](https://www.drupal.org/project/issues/admin_menu).

Reviewed MR!2, No issue found, file is updated as per the readme.md file template.

This for the outdated 8.1 branch - fixed it in 3 seconds myself for 2.x