Replace README.txt with README.md

Hi @goodboy

I think we can close this one as is already merged in the project repo.

Regards,
Andrei

Reviewed MR!4, The patch is not cleanly applied.

1. Project name is the first line of the document, and only level one heading (#).
2. [Project page] and [issue queue] is missing.
3. * is used in place of ( - )hyphen
4. Two lines prior to ##/### headings.
5. Links should have a meaningful link text, for example:
[Drupal](https://www.drupal.org/) (i.e. not just the URL)
6. 

This one is considered fixed as the MR was merged 7 months ago. Thx @goodboy

Automatically closed - issue fixed for 2 weeks with no activity.